American Journal of Industrial Medicine 19:327-337 (1991)
Occupation and the Occurrence of Testicular Cancer Stephen K. Van Den Eeden, MS, Noel S. Weiss, MD, DrPH, Clifton H. Strader, PhD, and Janet R. Daling, PhD
To investigate what role a man’s occupation may have on his risk of testicular cancer, we conducted a case-control study among noncryptorchid white males who were between 20 and 69 years of age and resided in western Washington State. Cases were men in whom a germ cell tumor of the testis was diagnosed between 1977 and 1984 (n = 323). Their occupational histories were compared to those of controls of the same age, race, and geographic area who were selected through random-digit dialing (n= 658). Administrators/managers (relative risk (RR) = 1.5), salesmen (RR = 1.5), electricians (RR = 2.8), and sailors and fishermen (RR = 3.1) were among the jobs reported more commonly by cases than controls. The risk among fannerdfarm managers was also elevated (RR = 1.9), but not that among farm workers (RR = 0.6). No consistent association between any one occupation and testicular cancer has been observed across studies of this topic. The most frequent observation has been an overrepresentation among cases of certain types of white collar worker; this may reflect the influence of some other aspect of socioeconomic status and not occupational exposures per se. Key words: testicular neoplasms, occupational diseases, occupation, testes
INTRODUCTION
Several reports have suggested that men engaged in some occupations may be at higher risk for testicular cancer. White collar or professional occupations have been associated with a moderately elevated risk [Graham and Gibson, 1972; Mustacchi and Millmore, 1976; Graham et al., 1977; Davies, 1981; Pearce et al., 19871, as has farming in some (but not all) studies [Graham and Gibson, 1972; Brown and Pottern, 1984; Mills et al., 1984; McDowall and Balarajan, 1986; Sewell et al., 1986; Wiklund et al., 1986; Pearce et al., 19871. Also, mechanics and repairmen [Ducatman et al., 1986; Pearce et al., 1987; Garland et al., 19881 and leather workers [Frumin et a]., 19891 have been noted in at least one study to have an elevated risk of testicular
Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington (S.K.V.D.E.,N.S.W., J.R.D.). Department of Epidemiology (SC-36), School of Public Health and Community Medicine, University of Washington, Seattle, Washington (S.K.V.D.E.,N.S. W., J.R.D.). Hanford Environmental Health Foundation, Richland, Washington (C.H.S.). Address reprint requests to Noel S. Weiss, MD, DrPH, Fred Hutchinson Cancer Research Center, 1124 Columbia (MP 381), Seattle, WA 98104. Accepted for publication August 13, 1990.
0 1991 Wiley-Liss, Inc.
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cancer. Ducatman et al. [ 19863 and Frumin et al. 119891 both suggested that exposure to the solvent dimethylformamide may be involved in the clusters of testicular cancer cases they studied. As part of a larger study of testicular cancer, we had an opportunity to evaluate what role a man’s occupation or industry of employment may have on his risk of testicular cancer. METHODS This analysis was based on data collected in a population-based case-control study of testicular cancer [Strader et al., 1988a, 1988b1. Using the Cancer Surveillance System, a tumor registry serving the 13 counties of western Washington State, we identified all living men aged 20 to 69 years who were diagnosed with a primary germ cell tumor of the testes between 1977 and 1984. Since a telephone interview was to be used, cases were required to live in a residence with a telephone and speak English. Cases were approached through their physician and an interview was conducted. Of 535 eligible cases, 56 (10.4%) of the patients were deceased; 48 (8.9%) refused to be interviewed; 13 (2.4%) were lost due to physician refusal to allow us to contact the subject; and 390 (72.4%) were interviewed. Nine cases that were not of germ cell origin were excluded from the analysis. As a basis for comparison, a random digit dialing technique [Waksberg, 19781 was employed to identify controls who resided in the same 13 counties as the cases, were 20 to 69 years old, lived in a residence with a telephone, and spoke English. A census was obtained for 87.7% (1,193/1,361) of the households contacted. Of 1,103 eligible controls identified, 209 (18.9%) refused to participate; 177 (16.0%) were lost to follow-up; and 729 (66.1%) were successfully interviewed. For purposes of this investigation, we excluded men who were not white and those who had a history of cryptorchism leaving 323 cases and 658 controls available for analysis. The interview was conducted by trained male interviewers who were assigned subjects without regard for case-control status, The interview included questions on demographic characteristics, genitourinary problems, previous history of vasectomy or cryptorchism, and an occupational and industrial history for the 10 year period prior to diagnosis for cases or interview for controls. Only jobs held for six months or longer were recorded. The occupational and industry history for each individual was coded by using the 1970 US Census Industry and Occupation Classification System [US Bureau of Census, 19711. With the assistance of an industrial hygienist, the coding was further collapsed into 51 occupational and 31 industrial categories based on the general categories of the census coding, to combine occupations or industries with similar exposures. This modification of the coding was done prior to the analysis and without regard to case-control status. Age-adjusted estimates of the relative risk were calculated by the method of Mantel and Haenszel [1959]. A test-based method was used to calculate 95% confidence intervals [Miettinen, 19761. When the exposed subjects were limited to either cases or controls, an exact method was used to calculate the 95% confidence interval [Mehta et al., 19851. RESULTS As compared to the controls, the men with testicular cancer tended to be younger, but were very similar with respect to marital status and educational attain-
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329
TABLE I. Selected Demographic Characteristics of Subjects in Evaluation of Occupation and Testicular Cancer, 1977-1984 Characteristic Age (years) 20-34 35-54 55-69 Marital status Single Married Divorced or widowed Unknown Highest level of education completed High school (16 years)
Cases n=323 (%)
Controls n=658 (%)
205 (63.5) 102 (31.6) 16 (5.0)
327 (49.7) 238 (36.2) 93 (14.1)
65 (20.1) 230 (71.2) 27 (8.4) 1 (0.3)
138 (21.0) 475 (72.2) 45 (6.8)
122 (37.8)
261 (39.7)
147 (45.5)
309 (47.0)
53 (16.4)
88 (13.4)
-
ment (Table I). Tables I1 and I11 present the distribution of cases and controls according to their occupation and industry of employment, respectively. In each analysis, the subject was classified first by his longest-held occupation and industry, and then by whether he had ever worked in a given occupation or industry. Hereafter, the results cited in this report will use estimates of the relative risk for ever having worked in a job or industry, except where noted. Among the white collar or professional occupations, men reporting ever having been an administrator or manager (RR = 1.5, 95% CI 1.1-2.2), salesmen or buyers (RR = 1.5, 95% CI 1.O-2.2), physicians and other health-diagnosing occupations (RR = 5.5, 95% CI 1.1-26.3), and other health treatment workers, such as physical and respiratory therapists (RR= 15.7, 95% CI 1.7-145.2), were found to have elevated relative risks. Among blue collar workers, men reporting ever working as electricians (RR = 2.8, 95% CI 1.2-6.4), sailors, deckhands, pilots and fishermen (RR=3.1, 95% CI 1.2-7.9), and handlers and laborers not otherwise classified (RR= 1.5, 95% CI 1.0-2.2) were more common among those with testicular cancer than among controls. Men who reported ever having been a vehicle mechanic had a decreased risk (RR=0.3, 95% CI 0.1-0.7). Men who reported working as a farmer and/or farm manager were found to have a 90% excess in risk relative to all other men (RR= 1.9, 95% CI 0.6-5.4). In contrast, subjects reporting having been a farm worker or gardener were found to have a decreased risk (RRz0.6, 95% CI 0.3-1.3). The relative risk for men reporting having worked in agriculture, forestry, or fishery industries was 1.0 (95% CI 0.6-1.6). Among the industrial categories, a greater proportion of cases than controls reported ever having worked in food product manufacturing (RR=2.2, 95% CI 1.0-4.9), metal product manufacturing (RR=2.0, 95% CI 1.O-3.8), and public administration (RR = 1.8, 95% 1.3-2.7).
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TABLE 11. Jobs (Longest- and Ever-Held) Held Longer Than 6 Months of Cases and Controls in Evaluation of Occupation and Testicular Cancer, 1987-1984 Longest - worked occupation (010) Occupation Administrator, manager Engineer, architect, surveyor Mathematical & computer scientist Natural scientist except chemist Chemist Flight crew Physician & other health diagnosing Other health treatment Educator, librarian, educational & vocational counselor Social, legal, recreational & religious worker Writer Photographer, designer, artist Health technician Engineering, science technician Other technician Sales & buyer Administrative support Protective service Food service Cleaning service except household Personal service Farm manager Farm worker & gardener Forestry, logging worker Sailor, deckhand, fisherman, pilot Vehicle mechanic
Cases Controls Relative n=323 n=658 Risk
Ever-worked occupation (%) 9 5 8 CI
Cases Controls Relative n=323 n=658 Risk
9 5 8 CI
14.6
10.9
1.6
1.1-2.5
18.0
13.7
1.5
1.1-2.2
2.8
4.3
0.7
0.3-1.4
4.3
5.2
0.8
0.4-1.6
0.9
I.5
0.6
0.2-2.3
1.9
2.0
1.0
0.3-4.0
0.3 0 0.3
0.8 0.2 0.6
0.5 0.4
0.1-3.7
0.9
1.1
0.3-4.0
-
0.3-16.5
1.6
0.9 0.2 1.1
1.4
0.4-4.6
0.6
0.3
2.2
0.3-16.5
1.6
0.3
5.5
1.1-26.3
0.6
0.2
10.6
0.9-121.5
0.9
0.2
15.7
1.7-145.2
2.5
3.0
0.9
0.4 -2.0
5.0
4.1
1.2
0.6-2.3
2.8 0
1.8 0.5
1.4
0.6-3.3 0
3. I 0.8
2.4
1.1
0.5-2.5
-
-
2.2 0.6
I .5 0.5
1.2 1.1
0.5-3 .O 0.2-6.3
3.7 9.
2.7 1.1
1.2 0.7
0.6-2.4 0.2-2.6
3.1 0.6 9.3
4.9 0.8 7.8
0.7 0.8 1.2
0.3-1.4 0.2-4. I 0.8-2.0
5.6 1.6 16.7
5.9 1.5 12.0
0.9 1.0 1.5
0.5-1.7 0.3-3.0 1.0-2.2
4.3 2.2 1.2
4.0 2.0 2.9
1.1 1 .0 0.4
0.6-2.0 0.4-2.7 0.1-1.1
7.7 3.7 5.9
7.0 3.0 6.7
1.0 1.1 0.7
0.6-1.6 0.5-2.3 0.4-1.3
0.9 0.6 1.2
2.0 0.3 0.8
0.5 1.8 1.5
0.1-2.0 0.2-1 3.6 0.4-6.2
1.90 0.6 2.2
3.8 0.9 1.4
0.5 0.5 1.9
0.2-1.1 0.1-2.7 0.6-5.4
0.9
2.4
0.3
0.1-1
3.7
4.7
0.6
0.3-1.3
0.9
0.9
1.1
0.2-5.1
2.2
1.7
1.2
0.4-3.4
I .2 0.9
0.2 3.2
6.9 0.3
1.2-41 . I 0.1-0.8
3.4 1.9
1.2 5.5
3.1 0.3
1.2-7.9 0.1-0.7
0
.o
(Continued)
Occupation and Testicular Cancer
331
TABLE 11. Jobs (Longest- and Ever-Held) Held Longer Than 6 Months of Cases and Controls in Evaluation of Occupation and Testicular Cancer, 1987-1984 (Continued) Longest-worked occupation (%) Occupation Industrial mechanic Electrical equipment mechanic Miscellaneous mechanics Carpenter Electrician Painter Plumber, pipefitter Other construction Extractive occupations Metalmaking worker Precision metal worker Other precision workers Metalworking machine operator Woodworking machine operator Textile machine operator Other machine operator Welder, cutter Other handworking occupation Production inspector Motor vehicle operator Other transportation Handler, laborer Service station attendant/helper Miscellaneous occupations Unknown occupations
Cases Controls Relative n=323 n=658 Risk
Ever-worked occupation (%)
95% CI
Cases Controls Relative n = 3 2 3 n=658 Risk
95% CI
2.5
2.9
0.9
0.4-2.0
0.9
1.7
0.5
0.2-1.8
0.5-2.2 0.5-2.0 1.0-6.1 0.3-3.1
5.3 7.4 4.0 2.8
5.3 5.8 1.4 1.8
1.1 1.2 2.8 1.3
0.6-2.0 0.7-2.0 1.2-6.4 0.6-3.2
1.3
0.4-5.0
1.9
1.1
1.7
0.5 -5.2
4.1
1.o
0.5-2.0
12.4
8.8
1.3
0.8 -2.0
0
0.2
-
0
0.5
0.3
0.5
0.5
0.1-4.9
0.9
0.5
1.6
0.3-7.9
1.2
1.4
1.o
0.3-3.6
1.9
I .5
1.3
1 .5-3.9
0.9
0.3
2.7
0.4-16.5
0.9
0.8
1.o
0.2-4.6
0.6
0.2
3.4
0.4-29.2
0.6
0.3
1.7
0.3-10.9
-
0
1.2
-
0.6
0.6
0.8
0.1-4.8
2.2
2.0
1.2
0
0.8
-
3.7 4.3 3.1 1.2
3.8 4.0 1.2 1.2
1.1 1 .o 2.4 0.9
1.2
0.9
4.3
0.5-3.0
0
0.3
-
2.5 0.9
1.7 1.4
1.4 0.8
0.6-3.5 0.2-3.0
5.3 1.2
3.8 2.1
1.20 0.6
0.7-2.3 0.2-1.8
0.3
0.3
0.9
0.1-8.2
0.3
0.8
0.4
0.1-2.4
0.3
0.8
0.4
0.1-4.1
1.7
1.1
1.8
0.6-5.8
4.6
5.0
0.9
0.5-1.8
9.6
1.8
1.2
0.7-1.9
0
0.6
-
0.6
0.8
0.9
0.7-1.9
8.0
5.8
1.2
0.7-2.1
16.7
10.3
1.5
1.0-2.2
0.3
0.3
1 .o
0.1-10.2
2.2
1.2
1.6
0.6-4.3
4.6 -
4.9 -
1.o 1.o
0.5-1.8 0.5-1.8
13.6 2.5
13.2 1.2
1.8 1.9
1.1-2.8 0.7-5.0
DISCUSSION There are several issues to keep in mind when interpreting these results. First, the absence of information on a number of potential subjects may have biased our
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Van Den Eeden et al.
TABLE 111. Industry Worked in (Longest- and Ever-Worked Longer Than 6 Months) of Cases and Controls in Evaluation of Occupation and Testicular Cancer, 1987-1984 Longest-worked (%) industry Agriculture, forestry, fisheries Mining and extracting Construction Manufacturing Food products Textile products Paper products Printing, publishing Chemicals Petroleumkoal refining & products Rubber, plastic products Leather, leather products Lumber, wood products Furniture, fixtures Stone, glass, concrete products Metdl products Machinery except electric Electrical products Transportation equipment Miscellaneous manufacturing Transportation, communication, utilities Wholesale trade Retail trade Financial, insurance, real estate, business services Repair services Personal services Entertainment, recreation Professional services Public administration Miscellaneous industries Never worked Unknown
Cases Controls Relative 11-323 n=658 Risk
Ever-worked (%)
95% CI
Cases Controls Relative n=323 n=658 Risk
95% C1
3.1
4.3
0.6
0.3-1.3
9.6
8.8
1.0
0.6-1.6
0 10.8
0.3 11.9
0.9
0.3 19.8
0.8 17.5
0.4
0.7-1.3
0.0-3.2 0.7-1.5
0.3
0.8 0 1.7
0.5 0.7
0.1-3.8
0 0.9
0.2-2.5
4.3 0 1.5
1.8 0 2.1
2.2 0 0.8
0.3-2.3
1.2 1.2
I .2 1.1
1.o 1.3
0.3-3.2 0.4-5. I
2.2 2.2
2.0 1.7
1.0 1.3
0.4-2.5 0.5-3.6
0.6
0.3
1.8
0.2-13.6
0.6
0.5
1.1
0.2-7.3
0
0
-
0.3
0.5
0.6
0.1-5.7
0
0
0
0
3.1 0
5.9 0
0.5 -
0.2-1
.o
7.1 0
7.9 0
0.8 -
0.5-1.4
0.6 2.5
0.5 1.8
1.2 1.4
0.2-7.1 0.6-3.7
0.9 5.3
0.6 2.7
1.4 2.0
0.3-5.8 1.0-3.8
2.8
2.1
I .4
0.6-3.3
3.1
3.3
0.9
0.4-2.0
1.9
1.5
1.1
0.4-3.1
2.5
2.3
1.0
0.4-2.2
7.7
7.6
1.1
0.6-1.8
11.4
1.2
0.8-1.7
1.2
0.8
1.6
0.4-6.2
1.9
1.2
1.5
0.5-4.3
11.1 3.1 13.3
9. I 4.4 8.2
1.3 0.7 1.6
0.8 -2 .0 0.3-1.4 1.O-2.4
15.8 5.9 23.5
12.5 5.3 19.2
1.3 1.0 1.1
0.9-1.9 0.6-1.9 0.8-1.5
9.0 I .6 0.9
10.5 3.5 0.3
0.9 0.4 3.5
0.6-1.4 0.2-1.1 0.5-24.1
13.9 3.7 2.5
14.6 5.0 1.1
1.0 0.7 2.0
0.7-1.4 0.3-1.4 0.7-5.8
1.9 11.5
1.4 13.4
1.2 0.8
0.4-3.1 0.5-1.2
4.0 16.1
2.9 18.4
1.2 0.8
0.6-2.3 0.6-1.1
8.4
6.7
1.4
0.8 -2.3
19.5
11.6
1.8
1.3-2.7
0 0 0
0 0 0
-
0 0
0 0 0.5
3.2
0.7-14.7
~
-
13.
1
4
I .L
1.1
1.0-4.9
Occupation and Testicular Cancer
333
results if non-participation was related differently for cases and controls to any of the occupations or industries. Second, the occupational and industrial history was obtained only for the prior ten year period. Occupations (part-time, summer) held outside this period were not ascertained and could potentially be important. However, because many of these men were relatively young, the ten year period often included the beginning of the man’s post-education employment. Third, the analysis did not account for latency of exposure. In grouping all subjects together regardless of when they were exposed, we may not have allowed adequate time to pass between exposure and the development of disease. Fourth, the categories used to classify occupation and industry likely contain workers with heterogeneous exposures. This misclassification would be non-differential and lead to attenuation of any real associations that may exist. Finally, the self-reported and retrospective ascertainment of exposure in this study introduces a concern about recall bias distorting our results. It is possible that the increased risks observed may be due, at least in part, to differential recall of occupational history by cases and controls. In comparing our results to those of other studies, the reader should bear in mind the different sources of data. In most previous studies of this association, occupational information has been obtained from data recorded in medical records [Mustacchi and Millmore, 19761, cancer registries [Jensen et al., 1984; Pearce et al., 1987; Sewell et al., 1986; Swerdlow and Skeet, 19881, or death certificates [McDowall and Balarajan, 19861. In contrast to the current study, these investigations were limited to using usual or most recent occupation or industry. White Collar or Professional Occupations
We found an excess risk of testicular cancer among administrators/managers (RR= 1.5,95% CI 1.1-2.2). Mustacchi and Millmore [1976] found that 10% of their cases and only 4% of their controls were managers. While Pearce et al. [1987], in a cancer-registry-based case-control study, found sales and service managers (RR=4.8, 95% CI 1.5-15.4) and production supervisors (RR=2.8, 95% CI 1.08.1) to be at excess risk, their broader category administrative/managerial occupations showed no excess (RR= 1.0, 95% CI 0.6-1.7). Swerdlow and Skeet [1988], also using cancer-registry-based cases and controls, found administrators and managers to have elevated risks. In contrast, a case-control study based on death certificates found no excess (RR=0.9, 95% CI 0.6-1.3) in the group classified as managers and company directors [McDowall and Balarajan, 19861. Our finding of an excess risk among salesmen and buyers is in agreement with two other studies [Pearce et al., 1987; Swerdlow and Skeet, 19881, although one of the studies found the increased risk limited to sales managers and service workers [Pearce et al., 19871. A study conducted at a referral oncology hospital reported no association between the occupation of salesman and testicular cancer [Mills et al., 19841. Four previous studies suggest that physicians or other health professionals may be at higher risk. Mustacchi and Millmore [1976] reported that there were three physicians, two dentists, one dental student, and one registered nurse among the cases in their study, while the only health professional among the controls was a medical student. Similarly, Pearce et al. [1987] reported an excess among medical, dental and veterinary workers (RR = 1.9) and attributed the excess to six cases among physicians (RR = 6.5, 95% CI 1.3-32.6). In two studies of different podiatric medical
334
Van Den Eeden et al.
schools, graduates were found to have an excess of testicular cancer compared to national cancer incidence data [Rose et al., 1983; Brahim et al., 19881. Unfortunately, other studies focusing on occupation and testicular cancer have not reported on this association. In our data, both health professionals who diagnose, such as physicians and dentists, and other health professionals, such as pharmacists and therapists, were also found to have elevated risks, although our estimates were rather imprecise due to the low prevalence of these occupations among men in our study. There were one physician, two dentists, one optometrist, one chiropractor, two pharmacists, one physical therapist, and one health technologist among the cases, whereas there were two physicians, one pharmacist, four health technologists, and no dentists, chiropractors, optometrists, or physical therapists among the controls. No cases or controls reported working as podiatrists. The basis for most of the associations of white collar occupations with testicular cancer is unclear. It is certainly possible that these associations may be due to circumstances not considered or characteristics as yet unknown of the men who engage in these occupations. Blue Collar Occupations
Men who had worked in several of the blue collar occupations were found to have elevated risks for testicular cancer. Our finding of a greater than two-fold increase in risk for electricians (RR= 2.8, 95% C1 1.2-6.4) contrasts with a mortality case-control study that found no elevation in risk (RR=0.9, 95% CI 0.6-1.3) [McDowall and Balarajan, 19861. Given the attention being placed on the role of electromagnetic fields in carcinogenesis, this association warrants further research. Other blue collar occupations with an elevated risk included sailors, deckhands, pilots and fishermen (RR = 3.1,95% CI 1.2-7.9), and laborers and handlers (RR = 1.5,95% CI 1 .O-2.2). McDowell and Balarajan [ 19861 reported no association between mortality from testicular cancer and working as a merchant Seaman. They also found a decreased risk for being a laborer not otherwise classified (RR = 0.71, 95% CI 0.540.94),while Pearce et al. [1987] found no association for laborers, production, or transport workers (RR= 1.05, 95% CI 0.83-1.33). In contrast to Pearce et al. [1987] and Garland et al. [1988], who reported elevated risks for motor mechanics (RR=2.0, 95% CI 0.9-4.4 and SIR=3.4, 95% CI 1.9-5.6, respectively), we found fewer than expected men with testicular cancer who had been a vehicle mechanic (RR=0.3, 95% CI 0.1-0.7). Ducatman et al. [ 19861 found an excess risk among naval aircraft repairmen in two repair facilities and not another. They hypothesized that exposure to dimethylformamidc (DMF) may be responsible for the excess since this solvent was only used at the two facilities with the clusters of testicular cancer. In our data, no cases and eight controls reported ever having work as an aircraft mechanic or repairman. If DMF exposure is related to testicular cancer, we may not have observed any excess if the aircraft mechanics and repairmen in the area covered by this study do not use this chemical. In an informal survey of several Seattle area commercial airline maintenance facilities and businesses that repair aircraft, supervisory personnel could not recall any use of this solvent. In a study conducted in Fulton County, New York [Frurnin et al., 19891, five of 10 cases and 17 of 129 controls had been employed in the leather industry. It was also hypothesized that dimethylformamide may have been the agent responsible for
Occupation and Testicular Cancer
335
the association since three of the cases which prompted the study all worked on the finishing line in a single tannery where DMF was used as a solvent. We were unable to evaluate the risk of testicular cancer among men working with leather since no subjects reported working in these occupations. However, data from Denmark failed to find any excess among leather industry workers [Olsen and Jensen, 19871. Farming Occupations
In our study, fannerdfarm managers were found to have an elevated risk (RR= 1.9, 95% CI 0.6-5.4), while farm workers and gardeners had a relative risk below one (RR=0.6, 95% CI 0.3-1.3). Further, men working in the agricultural industry had no excess of testicular cancer (RR= 1.0, 95% CI 0.6-1.6). Several studies have reported an elevated risk of testicular cancer in men working in agricultural occupations [Graham and Gibson, 1972; Mills et al., 19841, whereas other investigators have reported no association [Brown and Pottern, 1984; Jensen et al., 1984; Sewell et al., 1986; Olsen and Jensen, 19871. In a cohort study conducted in Sweden [Wiklund et al., 19861, the relative risk went from 0.83 in 1961-1966 to 1.35 in 1974-1979. Changes in farming practices were suggested as possible explanations for this latter finding. Two other studies, both case-control in design, classified agricultural workers similarly to the titles we used. McDowall and Balarajan [ 19861, in a study using death certificate data from England and Wales, reported the relative risk for fannerdfarm managers to be 1.8 (95% CI 1.1-3.1), while for farm workers it was 0.9 (95% CI 0.2-3.2). Pearce et al. [ 19871, in a study on cancer-registry data from New Zealand, reported the relative risks for fannerdfarmer managers and agricultural workers to be 1.1 (95% CI 0.7-1.8) and 0.5 (95% CI 0.2-1.2), respectively. Apart from chance, a possible explanation for this difference in risk between farmers and farm workers is that farmer/fann managers may have lived on the farm longer, especially during childhood and may have been exposed to the putative agent(s) longer. Alternatively, these results could reflect differences in the socioeconomic status (SES), in that fannerdfarm managers are likely to be of higher SES than farm workers, high SES having been found to be associated with an increased risk of testicular cancer [Graham and Gibson, 1972; Davies, 1981; Schottenfeld and Warshauer, 1982; Pearce et al., 19871. Industry We found that men reporting to ever have worked in the public administration (RR= 1.8, 95% CI 1.3-2.7), metal product manufacturing (RR=2.0, 95% CI 1.03.8), and food product manufacturing (RR=2.2, 95% CI 1.0-4.9) had an elevated risk of testicular cancer. Olsen and Jensen [1987], using cancer incidence data from Denmark, reported an excess among workers in public administration, particularly among local administration, and no increase in the other two categories. One other study reported no association with public administration [Mills et al., 19841. McDowall and Balarajan [1986] found an excess among food and beverage workers (RR = 1.82, 95% CI 1.04-3.19) while three other studies reported no association in similar workers [Olsen and Jensen, 1987; Pearce et al., 1987; Swerdlow and Skeet, 19881. In summary, these results, interpreted in conjunction with those of previous studies, fail to provide convincing evidence that any particular occupational exposure
336
Van Den Eeden et al.
bears on the incidcnce of testicular cancer. However, they do suggest several specific occupations whose association with testicular cancer would justify further, more refined, studies. Furthermore, as greater research emphasis is placed on the role of prenatal exposures in testicular cancer, parental occupational exposures should be examined. ACKNOWLEDGMENTS
This research was funded in part by grants No, 1-RO1-CA-30279-01 and 5R35-CA-39779. The assistance of Michael Morgan, PhD, Department of Environmental Sciences, and Thomas L. Vaughan, MD, MPH, Department of Epidemiology, University of Washington, with the classification of occupation is greatly appreciated. We are grateful to Dan Rock and Ken Scholcs for assistance in conducting this study. Portions of this paper were presented at the 20th Annual Meeting of the Society for Epidemiologic Research, Amherst, MA in June 1987, and at the 115th Annual Meeting of the American Public Health Association, New Orleans, LA, in November 1987. REFERENCES Brahirn F, Levinc B, Lerner A (1988): Testicular cancer in podiatrists. Curr Pod Med Nov.:17-18. Brown LM, Pottern LM (1984): Testicular cancer and farming (Letter). Lancet 1:1356. Davies JM (1981): Testicular cancer in England and Wales: some epidemiological aspects. Lancet 1:928-932. Ducatman AM, Conwill DE, Crawl J (1986): Germ cell tumors of the testicle among aircraft repairmen. J Urol 1361834-836, Frumin E, Brathwaite M, Townc W, Levin SM, Baker DB, Monaghan SV, Landrigan PJ, Marshall EG, Melius JM (1989): Testicular cancer in leather workers-Fulton County, New York. MMWR 38:105-106, 111-1 14. Garland FC, Gorham ED, Garland CF, Ducatman AM (1988): Tcsticular cancer in US Navy personnel. Am J Epidemiol 127:411-414. Graham S , Gibson RW (1972): Social epidemiology of cancer of the testis. Cancer 29:1242-1249. Graham S, Gibson R, West D, Swanson M, Burnett W, Dayal H (1 977): Epidemiology of cancer of the testis in upstate New York. JNCI 58:1255-1261. Jensen OM, Olsen JH, Osterlind A (1984): Testis cancer risk among farmers in Denmark (Letter). Lancet 1:794. Mantel N, Haenszel W (1959): Statistical aspects of the analysis of data from retrospective studies of disease. JNCI 22:719-748. Mehta CR, Patel NR, Gray R (1985): Computing an exact confidence interval for the common odds ratio in several 2 x 2 contingency tables. J Am Stat Assoc 80:969-973. McDowall ME, Balarajan K (1986): Testicular cancer mortality in England and Wales 1971-80: variations by occupation. J Epidemiol Comm Health 40:26-29. Miettincn 0s (1976): Estimability and estimation in case-referent studies. Am J Epidemiol 103:226-235. Mills PK, Newell GR, Johnson DE (1984): Testicular cancer associated with employment in agriculture and oil and natural gas extraction. Lancet 1:207-210. Mustacchi P, Millmore D (1976): Racial and occupational variations in cancer of the testis: San Francisco, 1956-65. JNCI 561717-720. Olsen JH, Jensen OM (1987): Occupation and risk of cancer in Denmark: An analysis of 93,810 cancer cases, 1970-1979. Scand J Work Environ Health (Suppl 1) 13:7-91. Pearce N, Sheppard RA, Howard JK, Fraser J , Lilley BM (1987): Time trends and occupational differences in cancer of the testis in New Zealand. Cancer 59:1677-1682. Rose LI, Weiss W, Gibley CW, Borowski G, Levy RA (1983): Carcinoma of the testis in podiatrists. Ann Int Med 99:636-637.
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Schottenfeld D, Warshauer ME (1982): Testis. In: Schottenfeld D, Fraumeni JF (eds): “Cancer Epidemiology and Prevention.” Saunders: Philadelphia, pp 947-957. Sewell CM, Castle SP, Hull HF, Wiggins C (1986): Testicular cancer and employment in agriculture and oil and natural gas extraction (Letter). Lancet 1553. Strader CH, Weiss NS, Daling JR, Karagas MR, McKnight B (198th): Cryptorchism, orchiopexy, and the risk of testicular cancer. Am J Epidemiol 127:1013-1018. Strader CH, Weiss NS, Daling JR (1988b): Vasectomy and the incidence of testicular cancer. Am J Epidemiol 12856-63. Swerdlow AJ, Skeet RG (1988): Occupational associations of testicular cancer in south east England. Br J Ind Med 45:225-230. US Bureau of Census (1971): “1970 Census of the Population, Classified Index of Industries and Occupations. ” Washington, DC: US Government Printing Office. Waksberg J (1978): Sampling methods for random digit dialing. J Am Stat Assoc 73:40-46. Wiklund K, Dish J, Holm L-E (1986): Testicular cancer among agricultural workers and licensed pesticide applicators in Sweden. Scand J Work Environ Health 12:630-631.
Occupation and the Occurrence of Testicular Cancer Stephen K. Van Den Eeden, MS, Noel S. Weiss, MD, DrPH, Clifton H. Strader, PhD, and Janet R. Daling, PhD
To investigate what role a man’s occupation may have on his risk of testicular cancer, we conducted a case-control study among noncryptorchid white males who were between 20 and 69 years of age and resided in western Washington State. Cases were men in whom a germ cell tumor of the testis was diagnosed between 1977 and 1984 (n = 323). Their occupational histories were compared to those of controls of the same age, race, and geographic area who were selected through random-digit dialing (n= 658). Administrators/managers (relative risk (RR) = 1.5), salesmen (RR = 1.5), electricians (RR = 2.8), and sailors and fishermen (RR = 3.1) were among the jobs reported more commonly by cases than controls. The risk among fannerdfarm managers was also elevated (RR = 1.9), but not that among farm workers (RR = 0.6). No consistent association between any one occupation and testicular cancer has been observed across studies of this topic. The most frequent observation has been an overrepresentation among cases of certain types of white collar worker; this may reflect the influence of some other aspect of socioeconomic status and not occupational exposures per se. Key words: testicular neoplasms, occupational diseases, occupation, testes
INTRODUCTION
Several reports have suggested that men engaged in some occupations may be at higher risk for testicular cancer. White collar or professional occupations have been associated with a moderately elevated risk [Graham and Gibson, 1972; Mustacchi and Millmore, 1976; Graham et al., 1977; Davies, 1981; Pearce et al., 19871, as has farming in some (but not all) studies [Graham and Gibson, 1972; Brown and Pottern, 1984; Mills et al., 1984; McDowall and Balarajan, 1986; Sewell et al., 1986; Wiklund et al., 1986; Pearce et al., 19871. Also, mechanics and repairmen [Ducatman et al., 1986; Pearce et al., 1987; Garland et al., 19881 and leather workers [Frumin et a]., 19891 have been noted in at least one study to have an elevated risk of testicular
Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington (S.K.V.D.E.,N.S.W., J.R.D.). Department of Epidemiology (SC-36), School of Public Health and Community Medicine, University of Washington, Seattle, Washington (S.K.V.D.E.,N.S. W., J.R.D.). Hanford Environmental Health Foundation, Richland, Washington (C.H.S.). Address reprint requests to Noel S. Weiss, MD, DrPH, Fred Hutchinson Cancer Research Center, 1124 Columbia (MP 381), Seattle, WA 98104. Accepted for publication August 13, 1990.
0 1991 Wiley-Liss, Inc.
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cancer. Ducatman et al. [ 19863 and Frumin et al. 119891 both suggested that exposure to the solvent dimethylformamide may be involved in the clusters of testicular cancer cases they studied. As part of a larger study of testicular cancer, we had an opportunity to evaluate what role a man’s occupation or industry of employment may have on his risk of testicular cancer. METHODS This analysis was based on data collected in a population-based case-control study of testicular cancer [Strader et al., 1988a, 1988b1. Using the Cancer Surveillance System, a tumor registry serving the 13 counties of western Washington State, we identified all living men aged 20 to 69 years who were diagnosed with a primary germ cell tumor of the testes between 1977 and 1984. Since a telephone interview was to be used, cases were required to live in a residence with a telephone and speak English. Cases were approached through their physician and an interview was conducted. Of 535 eligible cases, 56 (10.4%) of the patients were deceased; 48 (8.9%) refused to be interviewed; 13 (2.4%) were lost due to physician refusal to allow us to contact the subject; and 390 (72.4%) were interviewed. Nine cases that were not of germ cell origin were excluded from the analysis. As a basis for comparison, a random digit dialing technique [Waksberg, 19781 was employed to identify controls who resided in the same 13 counties as the cases, were 20 to 69 years old, lived in a residence with a telephone, and spoke English. A census was obtained for 87.7% (1,193/1,361) of the households contacted. Of 1,103 eligible controls identified, 209 (18.9%) refused to participate; 177 (16.0%) were lost to follow-up; and 729 (66.1%) were successfully interviewed. For purposes of this investigation, we excluded men who were not white and those who had a history of cryptorchism leaving 323 cases and 658 controls available for analysis. The interview was conducted by trained male interviewers who were assigned subjects without regard for case-control status, The interview included questions on demographic characteristics, genitourinary problems, previous history of vasectomy or cryptorchism, and an occupational and industrial history for the 10 year period prior to diagnosis for cases or interview for controls. Only jobs held for six months or longer were recorded. The occupational and industry history for each individual was coded by using the 1970 US Census Industry and Occupation Classification System [US Bureau of Census, 19711. With the assistance of an industrial hygienist, the coding was further collapsed into 51 occupational and 31 industrial categories based on the general categories of the census coding, to combine occupations or industries with similar exposures. This modification of the coding was done prior to the analysis and without regard to case-control status. Age-adjusted estimates of the relative risk were calculated by the method of Mantel and Haenszel [1959]. A test-based method was used to calculate 95% confidence intervals [Miettinen, 19761. When the exposed subjects were limited to either cases or controls, an exact method was used to calculate the 95% confidence interval [Mehta et al., 19851. RESULTS As compared to the controls, the men with testicular cancer tended to be younger, but were very similar with respect to marital status and educational attain-
Occupation and Testicular Cancer
329
TABLE I. Selected Demographic Characteristics of Subjects in Evaluation of Occupation and Testicular Cancer, 1977-1984 Characteristic Age (years) 20-34 35-54 55-69 Marital status Single Married Divorced or widowed Unknown Highest level of education completed High school (16 years)
Cases n=323 (%)
Controls n=658 (%)
205 (63.5) 102 (31.6) 16 (5.0)
327 (49.7) 238 (36.2) 93 (14.1)
65 (20.1) 230 (71.2) 27 (8.4) 1 (0.3)
138 (21.0) 475 (72.2) 45 (6.8)
122 (37.8)
261 (39.7)
147 (45.5)
309 (47.0)
53 (16.4)
88 (13.4)
-
ment (Table I). Tables I1 and I11 present the distribution of cases and controls according to their occupation and industry of employment, respectively. In each analysis, the subject was classified first by his longest-held occupation and industry, and then by whether he had ever worked in a given occupation or industry. Hereafter, the results cited in this report will use estimates of the relative risk for ever having worked in a job or industry, except where noted. Among the white collar or professional occupations, men reporting ever having been an administrator or manager (RR = 1.5, 95% CI 1.1-2.2), salesmen or buyers (RR = 1.5, 95% CI 1.O-2.2), physicians and other health-diagnosing occupations (RR = 5.5, 95% CI 1.1-26.3), and other health treatment workers, such as physical and respiratory therapists (RR= 15.7, 95% CI 1.7-145.2), were found to have elevated relative risks. Among blue collar workers, men reporting ever working as electricians (RR = 2.8, 95% CI 1.2-6.4), sailors, deckhands, pilots and fishermen (RR=3.1, 95% CI 1.2-7.9), and handlers and laborers not otherwise classified (RR= 1.5, 95% CI 1.0-2.2) were more common among those with testicular cancer than among controls. Men who reported ever having been a vehicle mechanic had a decreased risk (RR=0.3, 95% CI 0.1-0.7). Men who reported working as a farmer and/or farm manager were found to have a 90% excess in risk relative to all other men (RR= 1.9, 95% CI 0.6-5.4). In contrast, subjects reporting having been a farm worker or gardener were found to have a decreased risk (RRz0.6, 95% CI 0.3-1.3). The relative risk for men reporting having worked in agriculture, forestry, or fishery industries was 1.0 (95% CI 0.6-1.6). Among the industrial categories, a greater proportion of cases than controls reported ever having worked in food product manufacturing (RR=2.2, 95% CI 1.0-4.9), metal product manufacturing (RR=2.0, 95% CI 1.O-3.8), and public administration (RR = 1.8, 95% 1.3-2.7).
330
Van Den Eeden et al.
TABLE 11. Jobs (Longest- and Ever-Held) Held Longer Than 6 Months of Cases and Controls in Evaluation of Occupation and Testicular Cancer, 1987-1984 Longest - worked occupation (010) Occupation Administrator, manager Engineer, architect, surveyor Mathematical & computer scientist Natural scientist except chemist Chemist Flight crew Physician & other health diagnosing Other health treatment Educator, librarian, educational & vocational counselor Social, legal, recreational & religious worker Writer Photographer, designer, artist Health technician Engineering, science technician Other technician Sales & buyer Administrative support Protective service Food service Cleaning service except household Personal service Farm manager Farm worker & gardener Forestry, logging worker Sailor, deckhand, fisherman, pilot Vehicle mechanic
Cases Controls Relative n=323 n=658 Risk
Ever-worked occupation (%) 9 5 8 CI
Cases Controls Relative n=323 n=658 Risk
9 5 8 CI
14.6
10.9
1.6
1.1-2.5
18.0
13.7
1.5
1.1-2.2
2.8
4.3
0.7
0.3-1.4
4.3
5.2
0.8
0.4-1.6
0.9
I.5
0.6
0.2-2.3
1.9
2.0
1.0
0.3-4.0
0.3 0 0.3
0.8 0.2 0.6
0.5 0.4
0.1-3.7
0.9
1.1
0.3-4.0
-
0.3-16.5
1.6
0.9 0.2 1.1
1.4
0.4-4.6
0.6
0.3
2.2
0.3-16.5
1.6
0.3
5.5
1.1-26.3
0.6
0.2
10.6
0.9-121.5
0.9
0.2
15.7
1.7-145.2
2.5
3.0
0.9
0.4 -2.0
5.0
4.1
1.2
0.6-2.3
2.8 0
1.8 0.5
1.4
0.6-3.3 0
3. I 0.8
2.4
1.1
0.5-2.5
-
-
2.2 0.6
I .5 0.5
1.2 1.1
0.5-3 .O 0.2-6.3
3.7 9.
2.7 1.1
1.2 0.7
0.6-2.4 0.2-2.6
3.1 0.6 9.3
4.9 0.8 7.8
0.7 0.8 1.2
0.3-1.4 0.2-4. I 0.8-2.0
5.6 1.6 16.7
5.9 1.5 12.0
0.9 1.0 1.5
0.5-1.7 0.3-3.0 1.0-2.2
4.3 2.2 1.2
4.0 2.0 2.9
1.1 1 .0 0.4
0.6-2.0 0.4-2.7 0.1-1.1
7.7 3.7 5.9
7.0 3.0 6.7
1.0 1.1 0.7
0.6-1.6 0.5-2.3 0.4-1.3
0.9 0.6 1.2
2.0 0.3 0.8
0.5 1.8 1.5
0.1-2.0 0.2-1 3.6 0.4-6.2
1.90 0.6 2.2
3.8 0.9 1.4
0.5 0.5 1.9
0.2-1.1 0.1-2.7 0.6-5.4
0.9
2.4
0.3
0.1-1
3.7
4.7
0.6
0.3-1.3
0.9
0.9
1.1
0.2-5.1
2.2
1.7
1.2
0.4-3.4
I .2 0.9
0.2 3.2
6.9 0.3
1.2-41 . I 0.1-0.8
3.4 1.9
1.2 5.5
3.1 0.3
1.2-7.9 0.1-0.7
0
.o
(Continued)
Occupation and Testicular Cancer
331
TABLE 11. Jobs (Longest- and Ever-Held) Held Longer Than 6 Months of Cases and Controls in Evaluation of Occupation and Testicular Cancer, 1987-1984 (Continued) Longest-worked occupation (%) Occupation Industrial mechanic Electrical equipment mechanic Miscellaneous mechanics Carpenter Electrician Painter Plumber, pipefitter Other construction Extractive occupations Metalmaking worker Precision metal worker Other precision workers Metalworking machine operator Woodworking machine operator Textile machine operator Other machine operator Welder, cutter Other handworking occupation Production inspector Motor vehicle operator Other transportation Handler, laborer Service station attendant/helper Miscellaneous occupations Unknown occupations
Cases Controls Relative n=323 n=658 Risk
Ever-worked occupation (%)
95% CI
Cases Controls Relative n = 3 2 3 n=658 Risk
95% CI
2.5
2.9
0.9
0.4-2.0
0.9
1.7
0.5
0.2-1.8
0.5-2.2 0.5-2.0 1.0-6.1 0.3-3.1
5.3 7.4 4.0 2.8
5.3 5.8 1.4 1.8
1.1 1.2 2.8 1.3
0.6-2.0 0.7-2.0 1.2-6.4 0.6-3.2
1.3
0.4-5.0
1.9
1.1
1.7
0.5 -5.2
4.1
1.o
0.5-2.0
12.4
8.8
1.3
0.8 -2.0
0
0.2
-
0
0.5
0.3
0.5
0.5
0.1-4.9
0.9
0.5
1.6
0.3-7.9
1.2
1.4
1.o
0.3-3.6
1.9
I .5
1.3
1 .5-3.9
0.9
0.3
2.7
0.4-16.5
0.9
0.8
1.o
0.2-4.6
0.6
0.2
3.4
0.4-29.2
0.6
0.3
1.7
0.3-10.9
-
0
1.2
-
0.6
0.6
0.8
0.1-4.8
2.2
2.0
1.2
0
0.8
-
3.7 4.3 3.1 1.2
3.8 4.0 1.2 1.2
1.1 1 .o 2.4 0.9
1.2
0.9
4.3
0.5-3.0
0
0.3
-
2.5 0.9
1.7 1.4
1.4 0.8
0.6-3.5 0.2-3.0
5.3 1.2
3.8 2.1
1.20 0.6
0.7-2.3 0.2-1.8
0.3
0.3
0.9
0.1-8.2
0.3
0.8
0.4
0.1-2.4
0.3
0.8
0.4
0.1-4.1
1.7
1.1
1.8
0.6-5.8
4.6
5.0
0.9
0.5-1.8
9.6
1.8
1.2
0.7-1.9
0
0.6
-
0.6
0.8
0.9
0.7-1.9
8.0
5.8
1.2
0.7-2.1
16.7
10.3
1.5
1.0-2.2
0.3
0.3
1 .o
0.1-10.2
2.2
1.2
1.6
0.6-4.3
4.6 -
4.9 -
1.o 1.o
0.5-1.8 0.5-1.8
13.6 2.5
13.2 1.2
1.8 1.9
1.1-2.8 0.7-5.0
DISCUSSION There are several issues to keep in mind when interpreting these results. First, the absence of information on a number of potential subjects may have biased our
332
Van Den Eeden et al.
TABLE 111. Industry Worked in (Longest- and Ever-Worked Longer Than 6 Months) of Cases and Controls in Evaluation of Occupation and Testicular Cancer, 1987-1984 Longest-worked (%) industry Agriculture, forestry, fisheries Mining and extracting Construction Manufacturing Food products Textile products Paper products Printing, publishing Chemicals Petroleumkoal refining & products Rubber, plastic products Leather, leather products Lumber, wood products Furniture, fixtures Stone, glass, concrete products Metdl products Machinery except electric Electrical products Transportation equipment Miscellaneous manufacturing Transportation, communication, utilities Wholesale trade Retail trade Financial, insurance, real estate, business services Repair services Personal services Entertainment, recreation Professional services Public administration Miscellaneous industries Never worked Unknown
Cases Controls Relative 11-323 n=658 Risk
Ever-worked (%)
95% CI
Cases Controls Relative n=323 n=658 Risk
95% C1
3.1
4.3
0.6
0.3-1.3
9.6
8.8
1.0
0.6-1.6
0 10.8
0.3 11.9
0.9
0.3 19.8
0.8 17.5
0.4
0.7-1.3
0.0-3.2 0.7-1.5
0.3
0.8 0 1.7
0.5 0.7
0.1-3.8
0 0.9
0.2-2.5
4.3 0 1.5
1.8 0 2.1
2.2 0 0.8
0.3-2.3
1.2 1.2
I .2 1.1
1.o 1.3
0.3-3.2 0.4-5. I
2.2 2.2
2.0 1.7
1.0 1.3
0.4-2.5 0.5-3.6
0.6
0.3
1.8
0.2-13.6
0.6
0.5
1.1
0.2-7.3
0
0
-
0.3
0.5
0.6
0.1-5.7
0
0
0
0
3.1 0
5.9 0
0.5 -
0.2-1
.o
7.1 0
7.9 0
0.8 -
0.5-1.4
0.6 2.5
0.5 1.8
1.2 1.4
0.2-7.1 0.6-3.7
0.9 5.3
0.6 2.7
1.4 2.0
0.3-5.8 1.0-3.8
2.8
2.1
I .4
0.6-3.3
3.1
3.3
0.9
0.4-2.0
1.9
1.5
1.1
0.4-3.1
2.5
2.3
1.0
0.4-2.2
7.7
7.6
1.1
0.6-1.8
11.4
1.2
0.8-1.7
1.2
0.8
1.6
0.4-6.2
1.9
1.2
1.5
0.5-4.3
11.1 3.1 13.3
9. I 4.4 8.2
1.3 0.7 1.6
0.8 -2 .0 0.3-1.4 1.O-2.4
15.8 5.9 23.5
12.5 5.3 19.2
1.3 1.0 1.1
0.9-1.9 0.6-1.9 0.8-1.5
9.0 I .6 0.9
10.5 3.5 0.3
0.9 0.4 3.5
0.6-1.4 0.2-1.1 0.5-24.1
13.9 3.7 2.5
14.6 5.0 1.1
1.0 0.7 2.0
0.7-1.4 0.3-1.4 0.7-5.8
1.9 11.5
1.4 13.4
1.2 0.8
0.4-3.1 0.5-1.2
4.0 16.1
2.9 18.4
1.2 0.8
0.6-2.3 0.6-1.1
8.4
6.7
1.4
0.8 -2.3
19.5
11.6
1.8
1.3-2.7
0 0 0
0 0 0
-
0 0
0 0 0.5
3.2
0.7-14.7
~
-
13.
1
4
I .L
1.1
1.0-4.9
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results if non-participation was related differently for cases and controls to any of the occupations or industries. Second, the occupational and industrial history was obtained only for the prior ten year period. Occupations (part-time, summer) held outside this period were not ascertained and could potentially be important. However, because many of these men were relatively young, the ten year period often included the beginning of the man’s post-education employment. Third, the analysis did not account for latency of exposure. In grouping all subjects together regardless of when they were exposed, we may not have allowed adequate time to pass between exposure and the development of disease. Fourth, the categories used to classify occupation and industry likely contain workers with heterogeneous exposures. This misclassification would be non-differential and lead to attenuation of any real associations that may exist. Finally, the self-reported and retrospective ascertainment of exposure in this study introduces a concern about recall bias distorting our results. It is possible that the increased risks observed may be due, at least in part, to differential recall of occupational history by cases and controls. In comparing our results to those of other studies, the reader should bear in mind the different sources of data. In most previous studies of this association, occupational information has been obtained from data recorded in medical records [Mustacchi and Millmore, 19761, cancer registries [Jensen et al., 1984; Pearce et al., 1987; Sewell et al., 1986; Swerdlow and Skeet, 19881, or death certificates [McDowall and Balarajan, 19861. In contrast to the current study, these investigations were limited to using usual or most recent occupation or industry. White Collar or Professional Occupations
We found an excess risk of testicular cancer among administrators/managers (RR= 1.5,95% CI 1.1-2.2). Mustacchi and Millmore [1976] found that 10% of their cases and only 4% of their controls were managers. While Pearce et al. [1987], in a cancer-registry-based case-control study, found sales and service managers (RR=4.8, 95% CI 1.5-15.4) and production supervisors (RR=2.8, 95% CI 1.08.1) to be at excess risk, their broader category administrative/managerial occupations showed no excess (RR= 1.0, 95% CI 0.6-1.7). Swerdlow and Skeet [1988], also using cancer-registry-based cases and controls, found administrators and managers to have elevated risks. In contrast, a case-control study based on death certificates found no excess (RR=0.9, 95% CI 0.6-1.3) in the group classified as managers and company directors [McDowall and Balarajan, 19861. Our finding of an excess risk among salesmen and buyers is in agreement with two other studies [Pearce et al., 1987; Swerdlow and Skeet, 19881, although one of the studies found the increased risk limited to sales managers and service workers [Pearce et al., 19871. A study conducted at a referral oncology hospital reported no association between the occupation of salesman and testicular cancer [Mills et al., 19841. Four previous studies suggest that physicians or other health professionals may be at higher risk. Mustacchi and Millmore [1976] reported that there were three physicians, two dentists, one dental student, and one registered nurse among the cases in their study, while the only health professional among the controls was a medical student. Similarly, Pearce et al. [1987] reported an excess among medical, dental and veterinary workers (RR = 1.9) and attributed the excess to six cases among physicians (RR = 6.5, 95% CI 1.3-32.6). In two studies of different podiatric medical
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schools, graduates were found to have an excess of testicular cancer compared to national cancer incidence data [Rose et al., 1983; Brahim et al., 19881. Unfortunately, other studies focusing on occupation and testicular cancer have not reported on this association. In our data, both health professionals who diagnose, such as physicians and dentists, and other health professionals, such as pharmacists and therapists, were also found to have elevated risks, although our estimates were rather imprecise due to the low prevalence of these occupations among men in our study. There were one physician, two dentists, one optometrist, one chiropractor, two pharmacists, one physical therapist, and one health technologist among the cases, whereas there were two physicians, one pharmacist, four health technologists, and no dentists, chiropractors, optometrists, or physical therapists among the controls. No cases or controls reported working as podiatrists. The basis for most of the associations of white collar occupations with testicular cancer is unclear. It is certainly possible that these associations may be due to circumstances not considered or characteristics as yet unknown of the men who engage in these occupations. Blue Collar Occupations
Men who had worked in several of the blue collar occupations were found to have elevated risks for testicular cancer. Our finding of a greater than two-fold increase in risk for electricians (RR= 2.8, 95% C1 1.2-6.4) contrasts with a mortality case-control study that found no elevation in risk (RR=0.9, 95% CI 0.6-1.3) [McDowall and Balarajan, 19861. Given the attention being placed on the role of electromagnetic fields in carcinogenesis, this association warrants further research. Other blue collar occupations with an elevated risk included sailors, deckhands, pilots and fishermen (RR = 3.1,95% CI 1.2-7.9), and laborers and handlers (RR = 1.5,95% CI 1 .O-2.2). McDowell and Balarajan [ 19861 reported no association between mortality from testicular cancer and working as a merchant Seaman. They also found a decreased risk for being a laborer not otherwise classified (RR = 0.71, 95% CI 0.540.94),while Pearce et al. [1987] found no association for laborers, production, or transport workers (RR= 1.05, 95% CI 0.83-1.33). In contrast to Pearce et al. [1987] and Garland et al. [1988], who reported elevated risks for motor mechanics (RR=2.0, 95% CI 0.9-4.4 and SIR=3.4, 95% CI 1.9-5.6, respectively), we found fewer than expected men with testicular cancer who had been a vehicle mechanic (RR=0.3, 95% CI 0.1-0.7). Ducatman et al. [ 19861 found an excess risk among naval aircraft repairmen in two repair facilities and not another. They hypothesized that exposure to dimethylformamidc (DMF) may be responsible for the excess since this solvent was only used at the two facilities with the clusters of testicular cancer. In our data, no cases and eight controls reported ever having work as an aircraft mechanic or repairman. If DMF exposure is related to testicular cancer, we may not have observed any excess if the aircraft mechanics and repairmen in the area covered by this study do not use this chemical. In an informal survey of several Seattle area commercial airline maintenance facilities and businesses that repair aircraft, supervisory personnel could not recall any use of this solvent. In a study conducted in Fulton County, New York [Frurnin et al., 19891, five of 10 cases and 17 of 129 controls had been employed in the leather industry. It was also hypothesized that dimethylformamide may have been the agent responsible for
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the association since three of the cases which prompted the study all worked on the finishing line in a single tannery where DMF was used as a solvent. We were unable to evaluate the risk of testicular cancer among men working with leather since no subjects reported working in these occupations. However, data from Denmark failed to find any excess among leather industry workers [Olsen and Jensen, 19871. Farming Occupations
In our study, fannerdfarm managers were found to have an elevated risk (RR= 1.9, 95% CI 0.6-5.4), while farm workers and gardeners had a relative risk below one (RR=0.6, 95% CI 0.3-1.3). Further, men working in the agricultural industry had no excess of testicular cancer (RR= 1.0, 95% CI 0.6-1.6). Several studies have reported an elevated risk of testicular cancer in men working in agricultural occupations [Graham and Gibson, 1972; Mills et al., 19841, whereas other investigators have reported no association [Brown and Pottern, 1984; Jensen et al., 1984; Sewell et al., 1986; Olsen and Jensen, 19871. In a cohort study conducted in Sweden [Wiklund et al., 19861, the relative risk went from 0.83 in 1961-1966 to 1.35 in 1974-1979. Changes in farming practices were suggested as possible explanations for this latter finding. Two other studies, both case-control in design, classified agricultural workers similarly to the titles we used. McDowall and Balarajan [ 19861, in a study using death certificate data from England and Wales, reported the relative risk for fannerdfarm managers to be 1.8 (95% CI 1.1-3.1), while for farm workers it was 0.9 (95% CI 0.2-3.2). Pearce et al. [ 19871, in a study on cancer-registry data from New Zealand, reported the relative risks for fannerdfarmer managers and agricultural workers to be 1.1 (95% CI 0.7-1.8) and 0.5 (95% CI 0.2-1.2), respectively. Apart from chance, a possible explanation for this difference in risk between farmers and farm workers is that farmer/fann managers may have lived on the farm longer, especially during childhood and may have been exposed to the putative agent(s) longer. Alternatively, these results could reflect differences in the socioeconomic status (SES), in that fannerdfarm managers are likely to be of higher SES than farm workers, high SES having been found to be associated with an increased risk of testicular cancer [Graham and Gibson, 1972; Davies, 1981; Schottenfeld and Warshauer, 1982; Pearce et al., 19871. Industry We found that men reporting to ever have worked in the public administration (RR= 1.8, 95% CI 1.3-2.7), metal product manufacturing (RR=2.0, 95% CI 1.03.8), and food product manufacturing (RR=2.2, 95% CI 1.0-4.9) had an elevated risk of testicular cancer. Olsen and Jensen [1987], using cancer incidence data from Denmark, reported an excess among workers in public administration, particularly among local administration, and no increase in the other two categories. One other study reported no association with public administration [Mills et al., 19841. McDowall and Balarajan [1986] found an excess among food and beverage workers (RR = 1.82, 95% CI 1.04-3.19) while three other studies reported no association in similar workers [Olsen and Jensen, 1987; Pearce et al., 1987; Swerdlow and Skeet, 19881. In summary, these results, interpreted in conjunction with those of previous studies, fail to provide convincing evidence that any particular occupational exposure
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bears on the incidcnce of testicular cancer. However, they do suggest several specific occupations whose association with testicular cancer would justify further, more refined, studies. Furthermore, as greater research emphasis is placed on the role of prenatal exposures in testicular cancer, parental occupational exposures should be examined. ACKNOWLEDGMENTS
This research was funded in part by grants No, 1-RO1-CA-30279-01 and 5R35-CA-39779. The assistance of Michael Morgan, PhD, Department of Environmental Sciences, and Thomas L. Vaughan, MD, MPH, Department of Epidemiology, University of Washington, with the classification of occupation is greatly appreciated. We are grateful to Dan Rock and Ken Scholcs for assistance in conducting this study. Portions of this paper were presented at the 20th Annual Meeting of the Society for Epidemiologic Research, Amherst, MA in June 1987, and at the 115th Annual Meeting of the American Public Health Association, New Orleans, LA, in November 1987. REFERENCES Brahirn F, Levinc B, Lerner A (1988): Testicular cancer in podiatrists. Curr Pod Med Nov.:17-18. Brown LM, Pottern LM (1984): Testicular cancer and farming (Letter). Lancet 1:1356. Davies JM (1981): Testicular cancer in England and Wales: some epidemiological aspects. Lancet 1:928-932. Ducatman AM, Conwill DE, Crawl J (1986): Germ cell tumors of the testicle among aircraft repairmen. J Urol 1361834-836, Frumin E, Brathwaite M, Townc W, Levin SM, Baker DB, Monaghan SV, Landrigan PJ, Marshall EG, Melius JM (1989): Testicular cancer in leather workers-Fulton County, New York. MMWR 38:105-106, 111-1 14. Garland FC, Gorham ED, Garland CF, Ducatman AM (1988): Tcsticular cancer in US Navy personnel. Am J Epidemiol 127:411-414. Graham S , Gibson RW (1972): Social epidemiology of cancer of the testis. Cancer 29:1242-1249. Graham S, Gibson R, West D, Swanson M, Burnett W, Dayal H (1 977): Epidemiology of cancer of the testis in upstate New York. JNCI 58:1255-1261. Jensen OM, Olsen JH, Osterlind A (1984): Testis cancer risk among farmers in Denmark (Letter). Lancet 1:794. Mantel N, Haenszel W (1959): Statistical aspects of the analysis of data from retrospective studies of disease. JNCI 22:719-748. Mehta CR, Patel NR, Gray R (1985): Computing an exact confidence interval for the common odds ratio in several 2 x 2 contingency tables. J Am Stat Assoc 80:969-973. McDowall ME, Balarajan K (1986): Testicular cancer mortality in England and Wales 1971-80: variations by occupation. J Epidemiol Comm Health 40:26-29. Miettincn 0s (1976): Estimability and estimation in case-referent studies. Am J Epidemiol 103:226-235. Mills PK, Newell GR, Johnson DE (1984): Testicular cancer associated with employment in agriculture and oil and natural gas extraction. Lancet 1:207-210. Mustacchi P, Millmore D (1976): Racial and occupational variations in cancer of the testis: San Francisco, 1956-65. JNCI 561717-720. Olsen JH, Jensen OM (1987): Occupation and risk of cancer in Denmark: An analysis of 93,810 cancer cases, 1970-1979. Scand J Work Environ Health (Suppl 1) 13:7-91. Pearce N, Sheppard RA, Howard JK, Fraser J , Lilley BM (1987): Time trends and occupational differences in cancer of the testis in New Zealand. Cancer 59:1677-1682. Rose LI, Weiss W, Gibley CW, Borowski G, Levy RA (1983): Carcinoma of the testis in podiatrists. Ann Int Med 99:636-637.
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