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Ann. Rev. Med. 1979. 30:241-48 Copyright © 1979 by Annual Reviews 1nc. All rights reserved
BIG ACTH AND
.7319
Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
BRONCHOGENIC CARCINOMA Rosalyn S. Yalow, Ph.D. Solomon A. Berson Research Laboratory, Veterans Administration Hospital, Bronx, New York 10468; and The Mount Sinai School of Medicine, CUNY, New York, New York 10029
INTRODUCTION It is now commonly accepted that a variety of nonendocrine tumors are capable of elaborating one or more humoral substances that resemble well known, well-characterized, biologically active hormones or their prohor mone precursors or metabolic products (see 1-3 for reviews). These observations have promoted considerable interest in the potential of mass screening programs for early detection of malignancies. These programs would be based on measurement, generally by radioimmunoassay (RIA), of elevated concentrations of one or another of these hormonal forms in the circulating blood. Or such RIAs might provide objective measures of tumor responsiveness to various therapeutic procedures. This review considers the potential role of ACTH determinations in the diagnosis and management of patients with bronchogenic carcinoma since it is among such patients that ectopic Cushing's syndrome occurs most frequently (1).
CHARACTERIZATION OF ACTH IN TISSUE AND PLASMA In our early studies (4, 5) using RIA of plasma ACTH we did not notice any discrepancy between hormonal concentration and the clinical state or responsiveness to modulators of ACTH secretion. Nonetheless we subse quently observed (6) that in patients with pituitary Cushing's syndrome, plasma immunoreactive ACTH was generally considerably lower than in patients with ectopic Cushing'S syndrome. Similar observations were re241
0066-4219/79/0401-0241$0 l.OO
Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
242
YALOW
cently reported by Rees (7). The differences between the two groups of patients is now known to be related to the differences in the hormonal forms of immunoreactive ACTH in the circulation. Convincing evidence for the heterogeneity of other peptide hormones led us to investigate the nature of ACTH in plasma and tissue. We detected and characterized a new form of ACTH ("big ACTH"), which is larger and more acidic than the usual 1-39 peptide (8,9). The biologic activity of big ACTH was less than 4% of its immunologic activity (10). Although the usual 1-39 peptide generally predominates in the pituitary and in the plasma after pituitary stimulation,big ACTH is usually more prominent in plasma and tumor tissue of patients with ectopic hormone production (11). Odell et al (12) confirmed our findings with the demonstration that in a group of 38 patients with carcinoma and no clinical evidence of ectopic Cushing's syndrome immunoreactive ACTH is elevated, but biologically active ACTH, as determined in a receptor assay, is normal. Furthermore, Sephadex gel filtration of some of the plasmas from these patients revealed the presence of big ACTH. Orth et al (13) initially reported that extracts of the tumors in patients with ectopic ACTH syndrome contained an ACTH similar to pituitary ACTH and both N-terminal and C-terminal ACTH fragments. More recently this same group, using a different an tiserum,confirmed (14) that big ACTH predominated in extracts of tumors from two patients with ectopic Cushing'S syndrome and that no im munoreactive fragments smaller than the 1-39 peptide were noted. It would certainly have been of interest to determine the Sephadex elution profiles of these same extracts with the antisera they had previously employed to determine whether these new extracts contained ACTH fragments. It is now generally agreed that big ACTH of low biological activity is frequently a major component of plasma and tumor ACTH in patients with ectopic Cushing's syndrome. This resembles the findings that proinsulin is more prominent in tumor extracts and plasma of patients with islet cell tumors than in normal pancreatic tissue or plasma of other subjects (15,16). These observations suggest that in tumors there may be a defect in the conversion of prohormone to active hormone. This defect may arise from a qualitative or quantitative deficiency in the converting enzyme, a defect in the "packaging" of the enzyme together with the prohormone, which would inhibit enzymatic conversion, or the presence of an enzyme-inhibit ing factor in tumor tissue.
IMMUNOREACTIVE ACTH IN TISSUE EXTRACTS Observation of elevated plasma levels of ACTH due to ectopic hormone production is probably limited by the percentage of cases in which the tumor contains hormone in excess of that found in normal, nonendocrine,
Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
BIG ACTH AND BRONCHOGENIC CARCINOMA
243
nonmalignant tissue (11). It is,of course, possible for a tumor to secrete but be devoid of a hormone because of rapid turnover, but this is not generally so for peptide-hormone-secreting tumors. In our preliminary report (11) we were indeed surprised to detect ACTH in three bronchial adenomas and in 28 of 29 tissue samples (concentrations 4-55 nglg wet weight tissue) from carcinoma primary to or metastatic from the lung but not from tumors metastatic to the lung. In this small sampling we could not determine whether there was a relation between tumor type and hormone concentration since some were surgical specimens and others were obtained postmortem, often many hours after death. We subsequently noted (6) that although ACTH is found in all tumor types, the concentra tions in adenocarcinoma are generally significantly lower than in epider moid carcinoma (Figure 1). Since these 44 specimens were obtained at surgical resection, patients with small-cell undifferentiated ("oat" cell) car cinoma were not included in the group.
SQUAMOUS CELL CARCINOMA
ADENOCARCINOMA
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Range of concentrations of ACTH found in tumors of patients with squamous cell
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Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
244
YALOW
ACTH is not detectable « 1 ng/g wet weight tissue) in normal lung of man, dog, or rabbit. However, lung tissue from a "smoking" dog without invasive carcinoma but showing atypical histologic changes, including basal cell hyperplasia and atypical proliferation of alveolar lining cells, contained measurable levels of ACTH, primarily in the big form: lung tissue from three other "smoking" dogs with no significant histologic changes did not (11). (These tissues were obtained from Dr. Oscar Auerbach, East Orange Veterans Administration Hospital.) In another group of 19 patients, sampled at autopsy, immunoreactive ACTH was not detectable in normal areas of the lung. It ranged up to 34 ng/g in extracts of lung tumors; the highest values were in two patients with small-cell carcinoma. In these cases one cannot determine the possible losses in tissue ACTH between death and the time of sampling. ACTH was not detectable in a lymphoma or a renal cell carcinoma metastatic to the lung. Unexpected was the findings of levels up to 16 ng/g in areas of squamous metaplasia and suppurative bronchitis or pneumonia (R. Yalow et aI, previously unpublished observations). Thus, although ACTH is not detectable in normal lung tissue, it is found in some pathologic lung tissue even in the absence of invasive carcinoma. Important questions yet to be answered include: What is the insult to the lung and what is the extent of injury necessary to initiate elaboration of ACTH? Would bronchitis or pneumonia per se without the concomitant squamous metaplasia suffice? The need to determine at what stage in the progression from normalcy to invasive carcinoma in the lung parenchyma of smokers the ability to elaborate ACTH first occurs is evident from the classic work of Auerbach and associates (17). They noted on the basis of 20,000 sections from the tracheobronchial tree of over 400 autopsied cases that the percentage of cases in which carcinoma in situ was found in one or more sections was not very much different between very heavy smokers who died from lung cancer (83%) and those who did not (75%). Other changes in the lung parenchyma were also quite similar between these groups (17).
IMMUNOREACTIVE ACTH IN PLASMA Our observations that virtually all primary lung tumors contain ACTH and our initial demonstration that 21 of 24 patients with carcinoma of the lung untreated before sampling had afternoon plasma ACTH concentrations above 150 pg/ml, the upper limit achieved by only 6% of the control group, suggested the potential usefulness of plasma ACTH as a biologic marker for detection of lung cancer (11, 18). However, in a subsequent study (19) plasma ACTH was found to be elevated above 150 pg/ml in only 24 of 36 patients whose tumors were considered suitable for surgical resection. It
Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
BIG ACTH AND BRONCHOGENIC CARCINOMA
245
was elevated in only 66 of 136 patients randomized for chemotherapeutic protocols by the Veterans Administration Lung Group (6). Those with extensive disease appeared to exhibit elevated levels (59 of 107 cases) more frequently than those with limited disease, i.e. where the tumor was thought to be confined to one hemithorax, (11 of 29). In patients with ex tensive disease, those with adenocarcinoma exhibited elevated values less frequently (7 of 23) than those with other tumor types (52 of 84). This is consistent with the low concentrations of ACTH we found in ex tracts of adenocarcinoma compared to those of squamous cell carcinoma (Figure 1). Since the minimal concentration of ACTH detectable in tumors is only about one millionth that of the pituitary (11), the finding of false negatives is not surprising. If elevated values of plasma ACTH are derived from tumor ACTH then the tumor must be large, have a higher than minimally detectable hormone concentration, or be more active in secretion of the hormone than the pituitary. Since the metabolic turnover of the big ACTH may be markedly prolonged compared to the turnover of the 1-39 peptide, the relative plasma concentration of the big form compared to the usual form would be amplified by a factor equal to the relative turnover times. However, secretion of big ACTH is not suppressed by intravenous hy drocortisone under the same conditions as is the 1-39 peptide (11). There fore we do not know its disappearance rate and cannot determine this amplication factor. The greatest limitation of plasma ACTH assay for mass screening, as with all other "tumor marker" assays, is the potential for false positives, i.e. elevation of marker level in the absence of carcinoma. On occasion, sporadic release of pituitary ACTH can result in elevation of plasma ACTH even in normal subjects. The number of false positives on this basis can be reduced by multiple sampling in the afternoon when ACTH secretion is diminished, by the use of dexamethasone to suppress pituitary ACTH secretion, or by fractionation on Sephadex to ascertain the particular form of circulating ACTH. Thus distinction between a control group of nonsmokers and pa tients with lung carcinoma can generally be made. However, for diagnostic purposes the significant distinction to be made is between the very large group of heavy smokers without carcinoma and the very small group with carcinoma. Our earlier observations that even in the absence of proven carcinoma about one third of 36 patients with chronic obstructive pulmo nary disease have elevated plasma ACTH (18) suggested that a significant fraction of false positives might be found among heavy smokers. Further more lung tissues from a "smoking" dog with atypia (11) and from humans with squamous metaplasia, particularly with superimposed inflammatory processes, contain ACTH. Thus the ability to elaborate ACTH is manifest in injured but nonmalignant tissue.
246
YALOW
Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
The concept that in some patients the plasma ACTH cannot be derived solely from tumor ACTH is supported by data on the relationship between plasma and tumor ACTH (Figure 2). Although there seems to be some correlation between tumor concentration and plasma ACTH in many of the patients, there is a group with low tumor concentration and very high plasma levels. In these cases, at least, there must be a major contribution to plasma ACTH from nontumorous tissue, perhaps from areas in the lung with squamous metaplasia. Whether plasma ACTH changes can serve as a measure of response to various therapeutic modalities or as an indicator 1000
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Further
Quick links to online content
Ann. Rev. Med. 1979. 30:241-48 Copyright © 1979 by Annual Reviews 1nc. All rights reserved
BIG ACTH AND
.7319
Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
BRONCHOGENIC CARCINOMA Rosalyn S. Yalow, Ph.D. Solomon A. Berson Research Laboratory, Veterans Administration Hospital, Bronx, New York 10468; and The Mount Sinai School of Medicine, CUNY, New York, New York 10029
INTRODUCTION It is now commonly accepted that a variety of nonendocrine tumors are capable of elaborating one or more humoral substances that resemble well known, well-characterized, biologically active hormones or their prohor mone precursors or metabolic products (see 1-3 for reviews). These observations have promoted considerable interest in the potential of mass screening programs for early detection of malignancies. These programs would be based on measurement, generally by radioimmunoassay (RIA), of elevated concentrations of one or another of these hormonal forms in the circulating blood. Or such RIAs might provide objective measures of tumor responsiveness to various therapeutic procedures. This review considers the potential role of ACTH determinations in the diagnosis and management of patients with bronchogenic carcinoma since it is among such patients that ectopic Cushing's syndrome occurs most frequently (1).
CHARACTERIZATION OF ACTH IN TISSUE AND PLASMA In our early studies (4, 5) using RIA of plasma ACTH we did not notice any discrepancy between hormonal concentration and the clinical state or responsiveness to modulators of ACTH secretion. Nonetheless we subse quently observed (6) that in patients with pituitary Cushing's syndrome, plasma immunoreactive ACTH was generally considerably lower than in patients with ectopic Cushing'S syndrome. Similar observations were re241
0066-4219/79/0401-0241$0 l.OO
Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
242
YALOW
cently reported by Rees (7). The differences between the two groups of patients is now known to be related to the differences in the hormonal forms of immunoreactive ACTH in the circulation. Convincing evidence for the heterogeneity of other peptide hormones led us to investigate the nature of ACTH in plasma and tissue. We detected and characterized a new form of ACTH ("big ACTH"), which is larger and more acidic than the usual 1-39 peptide (8,9). The biologic activity of big ACTH was less than 4% of its immunologic activity (10). Although the usual 1-39 peptide generally predominates in the pituitary and in the plasma after pituitary stimulation,big ACTH is usually more prominent in plasma and tumor tissue of patients with ectopic hormone production (11). Odell et al (12) confirmed our findings with the demonstration that in a group of 38 patients with carcinoma and no clinical evidence of ectopic Cushing's syndrome immunoreactive ACTH is elevated, but biologically active ACTH, as determined in a receptor assay, is normal. Furthermore, Sephadex gel filtration of some of the plasmas from these patients revealed the presence of big ACTH. Orth et al (13) initially reported that extracts of the tumors in patients with ectopic ACTH syndrome contained an ACTH similar to pituitary ACTH and both N-terminal and C-terminal ACTH fragments. More recently this same group, using a different an tiserum,confirmed (14) that big ACTH predominated in extracts of tumors from two patients with ectopic Cushing'S syndrome and that no im munoreactive fragments smaller than the 1-39 peptide were noted. It would certainly have been of interest to determine the Sephadex elution profiles of these same extracts with the antisera they had previously employed to determine whether these new extracts contained ACTH fragments. It is now generally agreed that big ACTH of low biological activity is frequently a major component of plasma and tumor ACTH in patients with ectopic Cushing's syndrome. This resembles the findings that proinsulin is more prominent in tumor extracts and plasma of patients with islet cell tumors than in normal pancreatic tissue or plasma of other subjects (15,16). These observations suggest that in tumors there may be a defect in the conversion of prohormone to active hormone. This defect may arise from a qualitative or quantitative deficiency in the converting enzyme, a defect in the "packaging" of the enzyme together with the prohormone, which would inhibit enzymatic conversion, or the presence of an enzyme-inhibit ing factor in tumor tissue.
IMMUNOREACTIVE ACTH IN TISSUE EXTRACTS Observation of elevated plasma levels of ACTH due to ectopic hormone production is probably limited by the percentage of cases in which the tumor contains hormone in excess of that found in normal, nonendocrine,
Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
BIG ACTH AND BRONCHOGENIC CARCINOMA
243
nonmalignant tissue (11). It is,of course, possible for a tumor to secrete but be devoid of a hormone because of rapid turnover, but this is not generally so for peptide-hormone-secreting tumors. In our preliminary report (11) we were indeed surprised to detect ACTH in three bronchial adenomas and in 28 of 29 tissue samples (concentrations 4-55 nglg wet weight tissue) from carcinoma primary to or metastatic from the lung but not from tumors metastatic to the lung. In this small sampling we could not determine whether there was a relation between tumor type and hormone concentration since some were surgical specimens and others were obtained postmortem, often many hours after death. We subsequently noted (6) that although ACTH is found in all tumor types, the concentra tions in adenocarcinoma are generally significantly lower than in epider moid carcinoma (Figure 1). Since these 44 specimens were obtained at surgical resection, patients with small-cell undifferentiated ("oat" cell) car cinoma were not included in the group.
SQUAMOUS CELL CARCINOMA
ADENOCARCINOMA
•
30
•
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•
20
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Figure 1
•• • • •
,. "'..
a::: 0
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•
•
0
•• • • •
• • • •
.. ..... •
Range of concentrations of ACTH found in tumors of patients with squamous cell
carcinoma and adenocarcinoma of the lung but without Cushing's syndrome. (Reproduced from Ref. 6)
Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
244
YALOW
ACTH is not detectable « 1 ng/g wet weight tissue) in normal lung of man, dog, or rabbit. However, lung tissue from a "smoking" dog without invasive carcinoma but showing atypical histologic changes, including basal cell hyperplasia and atypical proliferation of alveolar lining cells, contained measurable levels of ACTH, primarily in the big form: lung tissue from three other "smoking" dogs with no significant histologic changes did not (11). (These tissues were obtained from Dr. Oscar Auerbach, East Orange Veterans Administration Hospital.) In another group of 19 patients, sampled at autopsy, immunoreactive ACTH was not detectable in normal areas of the lung. It ranged up to 34 ng/g in extracts of lung tumors; the highest values were in two patients with small-cell carcinoma. In these cases one cannot determine the possible losses in tissue ACTH between death and the time of sampling. ACTH was not detectable in a lymphoma or a renal cell carcinoma metastatic to the lung. Unexpected was the findings of levels up to 16 ng/g in areas of squamous metaplasia and suppurative bronchitis or pneumonia (R. Yalow et aI, previously unpublished observations). Thus, although ACTH is not detectable in normal lung tissue, it is found in some pathologic lung tissue even in the absence of invasive carcinoma. Important questions yet to be answered include: What is the insult to the lung and what is the extent of injury necessary to initiate elaboration of ACTH? Would bronchitis or pneumonia per se without the concomitant squamous metaplasia suffice? The need to determine at what stage in the progression from normalcy to invasive carcinoma in the lung parenchyma of smokers the ability to elaborate ACTH first occurs is evident from the classic work of Auerbach and associates (17). They noted on the basis of 20,000 sections from the tracheobronchial tree of over 400 autopsied cases that the percentage of cases in which carcinoma in situ was found in one or more sections was not very much different between very heavy smokers who died from lung cancer (83%) and those who did not (75%). Other changes in the lung parenchyma were also quite similar between these groups (17).
IMMUNOREACTIVE ACTH IN PLASMA Our observations that virtually all primary lung tumors contain ACTH and our initial demonstration that 21 of 24 patients with carcinoma of the lung untreated before sampling had afternoon plasma ACTH concentrations above 150 pg/ml, the upper limit achieved by only 6% of the control group, suggested the potential usefulness of plasma ACTH as a biologic marker for detection of lung cancer (11, 18). However, in a subsequent study (19) plasma ACTH was found to be elevated above 150 pg/ml in only 24 of 36 patients whose tumors were considered suitable for surgical resection. It
Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
BIG ACTH AND BRONCHOGENIC CARCINOMA
245
was elevated in only 66 of 136 patients randomized for chemotherapeutic protocols by the Veterans Administration Lung Group (6). Those with extensive disease appeared to exhibit elevated levels (59 of 107 cases) more frequently than those with limited disease, i.e. where the tumor was thought to be confined to one hemithorax, (11 of 29). In patients with ex tensive disease, those with adenocarcinoma exhibited elevated values less frequently (7 of 23) than those with other tumor types (52 of 84). This is consistent with the low concentrations of ACTH we found in ex tracts of adenocarcinoma compared to those of squamous cell carcinoma (Figure 1). Since the minimal concentration of ACTH detectable in tumors is only about one millionth that of the pituitary (11), the finding of false negatives is not surprising. If elevated values of plasma ACTH are derived from tumor ACTH then the tumor must be large, have a higher than minimally detectable hormone concentration, or be more active in secretion of the hormone than the pituitary. Since the metabolic turnover of the big ACTH may be markedly prolonged compared to the turnover of the 1-39 peptide, the relative plasma concentration of the big form compared to the usual form would be amplified by a factor equal to the relative turnover times. However, secretion of big ACTH is not suppressed by intravenous hy drocortisone under the same conditions as is the 1-39 peptide (11). There fore we do not know its disappearance rate and cannot determine this amplication factor. The greatest limitation of plasma ACTH assay for mass screening, as with all other "tumor marker" assays, is the potential for false positives, i.e. elevation of marker level in the absence of carcinoma. On occasion, sporadic release of pituitary ACTH can result in elevation of plasma ACTH even in normal subjects. The number of false positives on this basis can be reduced by multiple sampling in the afternoon when ACTH secretion is diminished, by the use of dexamethasone to suppress pituitary ACTH secretion, or by fractionation on Sephadex to ascertain the particular form of circulating ACTH. Thus distinction between a control group of nonsmokers and pa tients with lung carcinoma can generally be made. However, for diagnostic purposes the significant distinction to be made is between the very large group of heavy smokers without carcinoma and the very small group with carcinoma. Our earlier observations that even in the absence of proven carcinoma about one third of 36 patients with chronic obstructive pulmo nary disease have elevated plasma ACTH (18) suggested that a significant fraction of false positives might be found among heavy smokers. Further more lung tissues from a "smoking" dog with atypia (11) and from humans with squamous metaplasia, particularly with superimposed inflammatory processes, contain ACTH. Thus the ability to elaborate ACTH is manifest in injured but nonmalignant tissue.
246
YALOW
Annu. Rev. Med. 1979.30:241-248. Downloaded from www.annualreviews.org Access provided by McMaster University on 02/14/15. For personal use only.
The concept that in some patients the plasma ACTH cannot be derived solely from tumor ACTH is supported by data on the relationship between plasma and tumor ACTH (Figure 2). Although there seems to be some correlation between tumor concentration and plasma ACTH in many of the patients, there is a group with low tumor concentration and very high plasma levels. In these cases, at least, there must be a major contribution to plasma ACTH from nontumorous tissue, perhaps from areas in the lung with squamous metaplasia. Whether plasma ACTH changes can serve as a measure of response to various therapeutic modalities or as an indicator 1000
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