REPORTS Screening Sigmoidoscopy and Colorectal Cancer Mortality
Although screening tests to reduce colorectal cancer mortality are widely advocated and intuitively attractive, evidence supporting their usefulness is limited (1,2). Three techniques available to detect colorectal cancer are fecal occult blood testing, digital rectal examination, and sigmoidoscopy. Of these methods, sigmoidoscopy has shown the most promise for effectively reducing colorectal cancer mortality. The advantages of this screening technique are that it allows early detection of tumors in the rectum and distal colon and that it can be used to identify and remove adenomatous polyps (5-5). Despite the highly sensitive nature of sigmoidoscopy, there are not yet conclusive data from controlled clinical trials to support the efficacy of this method (6,7). The strongest supportive evidence to date is provided by a recent case-control study (8) in which screening sigmoidoscopy was associated with a 60% reduction in colorectal mortality. Although the application of case-control methods to the evaluation of screening efficacy is complex (9-14), careful selection of subjects and complete screening and followup data can minimize bias. Here, we describe a case-control study designed to evaluate the efficacy of screening sigmoidoscopy in reduction of colorectal cancer mortality.
Background: Sigmoidoscopy may reduce colorectal cancer mortality by identifying both cancers and precursor lesions (including polyps) for treatment; however, evidence regarding the efficacy of this technique as a screening procedure is extremely limited. Purpose: In the absence of data from randomized controlled trials, we performed a retrospective casecontrol study to determine if sigmoidoscopy screening is associated with a reduction in colorectal cancer mortality. Methods: The medical records of 66 members of the Greater Marshfield Community Health Plan (GMCHP) who died of large-bowel cancer from 1979 to 1988 were reviewed for history of screening for colorectal cancer (case subjects). For comparison, the records of 196 GMCHP members of similar gender, age, and enrollment duration were randomly selected for review (control subjects). Results: History of screening sigmoidoscopy was much less common among case subjects (10%) than among control subjects (30%). Risk for death from colorectal cancer was reduced among individuals having had a single examination by screening sigmoidoscopy (odds ratio = 0.21; 95% confidence interval = 0.08-0.52), compared with the risk for Subjects and Methods those who never had one. The reduction in risk appeared to be limited to Subjects for this institutionally aptumors in the rectum and distal colon. proved retrospective study were selected Neither fecal occult blood testing nor from records of members of the Greater digital rectal examination was associ- Marshfield Community Health Plan 1572
(GMCHP) during the study period 1979 to 1988. GMCHP is a prepaid health plan of 63 000 people. Case subjects were men and women who died of cancer of the colon or the rectum during this period. The cause of death had to be confirmed by both tumor registry records and death certificate review. If discordancies were found, they were resolved by a medical record review completed by a physician external to the study, William Paul, M.D. To be eligible for this study, subjects had to be enrolled in the health plan at least 12 months prior to diagnosis. Control subjects were randomly selected from GMCHP membership files to match the age (within 1 year), sex, and enrollment periods of the case subjects. Three control subjects were selected for each eligible case subject. Screening history was determined exclusively through review of the combined hospital and clinic medical records. For each eligible case subject and control subject, information was collected on dates, signs and symptoms, and results of fecal occult blood testing, digital rectal examination, and sigmoidoscopy. For fecal occult blood testing, the
Received March 9, 1992; revised July 13, 1992; accepted July 21, 1992. Supported by Public Health Service grant CA-46559 from the National Cancer Institute, National Institutes of Health, Department of Health and Human Services. An earlier version of this report was presented at the 22nd Annual Meeting of the Society for Epidemiologic Research, Birmingham, Ala., June 1989. P. A. Newcomb, B. E. Storer, T. S. Surawicz, P. M. Marcus, University of Wisconsin Comprehensive Cancer Center, Madison. R. G. Norfleet, Division of Gastroenterology, Marshfield Clinic, Marshfield, Wis. We thank the staff of the Marshfield Medical Foundation and the Medical Records Department at the Marshfield Clinic for their support, Dr. William Paul for technical advice, and Dr. Noel S. Weiss for stimulating discussions.
*Correspondence to: Polly A. Newcomb, Ph.D., University of Wisconsin Comprehensive Cancer Center, 1300 University Ave. #6795, Madison, WI 53706. Journal of the National Cancer Institute
Downloaded from http://jnci.oxfordjournals.org/ at University of Bath Library & Learning Centre on July 12, 2015
Polly A. Newcomb, * Robert G. Norfleet, Barry E. Storer, Tanya S. Surawicz, Pam M. Marcus
ated with a reduction in colorectal cancer mortality. Conclusions: These results suggest that screening sigmoidoscopy can substantially reduce mortality from cancers of the rectum and distal colon. [J Natl Cancer Inst 84:1572-1575, 1992]
Table 1. Characteristics of case subjects with death attributable to colorectal cancer and of control subjects
Of the 74 case subjects who met the eligibility criteria, 66 had medical records available and were included in the analysis. Of the 206 original control subjects selected for analysis, 10 were excluded. Medical records were unobtainable for eight, and two with previous colon cancer could not be matched to a case subject's date of diagnosis. These exclusions yielded 196 control subjects for analysis. The distribution of age, sex, Vol. 84, No. 20, October 21, 1992
Control subjects (n = 196)*
Case subjects (n = 66)
No.
%
No.
%
Age at diagnosis or at reference time, y
Although screening tests to reduce colorectal cancer mortality are widely advocated and intuitively attractive, evidence supporting their usefulness is limited (1,2). Three techniques available to detect colorectal cancer are fecal occult blood testing, digital rectal examination, and sigmoidoscopy. Of these methods, sigmoidoscopy has shown the most promise for effectively reducing colorectal cancer mortality. The advantages of this screening technique are that it allows early detection of tumors in the rectum and distal colon and that it can be used to identify and remove adenomatous polyps (5-5). Despite the highly sensitive nature of sigmoidoscopy, there are not yet conclusive data from controlled clinical trials to support the efficacy of this method (6,7). The strongest supportive evidence to date is provided by a recent case-control study (8) in which screening sigmoidoscopy was associated with a 60% reduction in colorectal mortality. Although the application of case-control methods to the evaluation of screening efficacy is complex (9-14), careful selection of subjects and complete screening and followup data can minimize bias. Here, we describe a case-control study designed to evaluate the efficacy of screening sigmoidoscopy in reduction of colorectal cancer mortality.
Background: Sigmoidoscopy may reduce colorectal cancer mortality by identifying both cancers and precursor lesions (including polyps) for treatment; however, evidence regarding the efficacy of this technique as a screening procedure is extremely limited. Purpose: In the absence of data from randomized controlled trials, we performed a retrospective casecontrol study to determine if sigmoidoscopy screening is associated with a reduction in colorectal cancer mortality. Methods: The medical records of 66 members of the Greater Marshfield Community Health Plan (GMCHP) who died of large-bowel cancer from 1979 to 1988 were reviewed for history of screening for colorectal cancer (case subjects). For comparison, the records of 196 GMCHP members of similar gender, age, and enrollment duration were randomly selected for review (control subjects). Results: History of screening sigmoidoscopy was much less common among case subjects (10%) than among control subjects (30%). Risk for death from colorectal cancer was reduced among individuals having had a single examination by screening sigmoidoscopy (odds ratio = 0.21; 95% confidence interval = 0.08-0.52), compared with the risk for Subjects and Methods those who never had one. The reduction in risk appeared to be limited to Subjects for this institutionally aptumors in the rectum and distal colon. proved retrospective study were selected Neither fecal occult blood testing nor from records of members of the Greater digital rectal examination was associ- Marshfield Community Health Plan 1572
(GMCHP) during the study period 1979 to 1988. GMCHP is a prepaid health plan of 63 000 people. Case subjects were men and women who died of cancer of the colon or the rectum during this period. The cause of death had to be confirmed by both tumor registry records and death certificate review. If discordancies were found, they were resolved by a medical record review completed by a physician external to the study, William Paul, M.D. To be eligible for this study, subjects had to be enrolled in the health plan at least 12 months prior to diagnosis. Control subjects were randomly selected from GMCHP membership files to match the age (within 1 year), sex, and enrollment periods of the case subjects. Three control subjects were selected for each eligible case subject. Screening history was determined exclusively through review of the combined hospital and clinic medical records. For each eligible case subject and control subject, information was collected on dates, signs and symptoms, and results of fecal occult blood testing, digital rectal examination, and sigmoidoscopy. For fecal occult blood testing, the
Received March 9, 1992; revised July 13, 1992; accepted July 21, 1992. Supported by Public Health Service grant CA-46559 from the National Cancer Institute, National Institutes of Health, Department of Health and Human Services. An earlier version of this report was presented at the 22nd Annual Meeting of the Society for Epidemiologic Research, Birmingham, Ala., June 1989. P. A. Newcomb, B. E. Storer, T. S. Surawicz, P. M. Marcus, University of Wisconsin Comprehensive Cancer Center, Madison. R. G. Norfleet, Division of Gastroenterology, Marshfield Clinic, Marshfield, Wis. We thank the staff of the Marshfield Medical Foundation and the Medical Records Department at the Marshfield Clinic for their support, Dr. William Paul for technical advice, and Dr. Noel S. Weiss for stimulating discussions.
*Correspondence to: Polly A. Newcomb, Ph.D., University of Wisconsin Comprehensive Cancer Center, 1300 University Ave. #6795, Madison, WI 53706. Journal of the National Cancer Institute
Downloaded from http://jnci.oxfordjournals.org/ at University of Bath Library & Learning Centre on July 12, 2015
Polly A. Newcomb, * Robert G. Norfleet, Barry E. Storer, Tanya S. Surawicz, Pam M. Marcus
ated with a reduction in colorectal cancer mortality. Conclusions: These results suggest that screening sigmoidoscopy can substantially reduce mortality from cancers of the rectum and distal colon. [J Natl Cancer Inst 84:1572-1575, 1992]
Table 1. Characteristics of case subjects with death attributable to colorectal cancer and of control subjects
Of the 74 case subjects who met the eligibility criteria, 66 had medical records available and were included in the analysis. Of the 206 original control subjects selected for analysis, 10 were excluded. Medical records were unobtainable for eight, and two with previous colon cancer could not be matched to a case subject's date of diagnosis. These exclusions yielded 196 control subjects for analysis. The distribution of age, sex, Vol. 84, No. 20, October 21, 1992
Control subjects (n = 196)*
Case subjects (n = 66)
No.
%
No.
%
Age at diagnosis or at reference time, y
