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Cancer Epidemiology Centre, Anti-Cancer Council of Victoria, Melbourne, VIC 3053 Australia [G. G. G., D. R. E.]; Division of Epidemiology and Biostatistics, European Institute of Oncology, 1-20141, Milan, Italy [G. S., P. B.]; Department of Dermatology, St. Vincents Hospital, Melbourne, VIC 3065 Australia [R. S.]; Department of Preventive and Social Medicine, Dunedin Medical School, University of Otago, New Zealand 9001 [M. R. E. M.]; Cancer Epidemiology Research Unit, New South Wales Cancer Council, Sydney, 2011 New South Wales, Australia [M. R. E. M.]; Department of Public Health, University of Western Australia, Perth, 6009 Australia [D. R. E.]; Royal Melbourne Hospital, Melbourne, 3052 Australia [W. J.]; and Centre for Genetic Epidemiology, University of Melbourne, Melbourne, 3052 Australia [J. L. H.]
| Abstract |
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| Introduction |
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Androgens exert their effects by binding to a single cytoplasmic AR, and their potency is determined by the binding affinity to the AR, with DHT binding five times more strongly than T (2)
. The enzyme 5
R converts T to its active form, DHT. DHT is implicated not only in the development of benign prostatic hypertrophy but also in the pathogenesis of prostate cancer (3
, 4)
. Isozymes of 5
R are differentially expressed in tissues; 5
R-1 is expressed in the skin, sebaceous glands, liver, adrenal, and kidney, whereas 5
R-2 is expressed in the prostate, testes, seminal vesicles, liver, and hair follicles (5
, 6)
. Inherited deficiency of 5
R-2 leads to absence of AA and a small prostate (7)
. Finasteride, a 5
R-2 inhibitor with little 5
R-1 activity, has been useful in the treatment of AA and benign prostatic hypertrophy (8
, 9)
. Finasteride down-regulates expression and secretion of PSA (10)
, but its short-term use in the chemoprevention of prostate cancer, benign prostatic hypertrophy, and elevated PSA has not been successful (11)
, and long-term use is still subject to trial (12)
. Studies that have specifically addressed the question of whether AA is associated with prostate cancer are few and have produced inconsistent findings (13, 14, 15, 16, 17)
. We examined associations of AA with early-onset, moderate- to high-grade prostate cancer in a large case-control study (18)
. The main thrust of the case-control study was to examine lifestyle associations with the diagnosis of "clinically important" prostate cancer. To this end, we excluded tumors that were well differentiated (low grade or Gleason score <5). We also focused on early-onset cancers because we were interested in finding factors relevant to the prevention of prostate cancer in men before the age of 70.
| Materials and Methods |
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Eligible cases comprised all male residents of Melbourne, Sydney, and Perth diagnosed from 1994 to 1997 and recorded in the population-based cancer registries with a histopathology-confirmed diagnosis of adenocarcinoma of the prostate (International Classification of Diseases, 9th revision, rubric 185), excluding well-differentiated tumors (defined as low grade, i.e., those with Gleason scores <5). Cases had to be <70 years of age at diagnosis and also had to be registered to vote on the state electoral rolls (adult registration to vote is compulsory in Australia). Meeting this criteria, all cases diagnosed before the age of 60 years were included, and random samples of 50% of cases diagnosed at 6064 years of age and 25% of cases diagnosed at 6569 years of age were selected, with the proportions varying over time to fit interview quotas.
Controls were randomly selected from men on the current state electoral rolls and were frequency matched to the predicted age distribution of the cases in a ratio of one control per case. Potential controls were matched against the cancer registries at the time of recruitment to exclude men with a known history of prostate cancer. Controls were identified and interviewed contemporaneously with the cases over the period 1994 to 1997. During the course of this study, 3 controls were subsequently diagnosed with prostate cancer and were selected as eligible cases. These subjects are included as cases and as controls.
After seeking advice from the case subjects urologists, from whom some clinical details were sought, we wrote to each subject inviting him to participate. We wrote to the control subjects directly. Face-to-face interviews were arranged, usually at the mans home. A structured interview schedule was used to obtain information on lifestyle exposures and personal attributes. While the subject was completing a sexual history questionnaire in private, the interviewer scored the subjects AA according to a set of four pictures (Fig. 1)
adapted from the Hamilton-Norwood scale (19)
. The first picture shows essentially no balding (Hamilton-Norwood stages I and II), the second shows frontal balding (Hamilton-Norwood stages II, III, IIIa, and IVa), the third shows vertex balding (Hamilton-Norwood stage III vertex-V), and the fourth shows frontal baldness concurrent with vertex baldness (Hamilton-Norwood stage IV, V, Va, VI, and VII).
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Given that smoking and educational status may be predictors of response, we assessed the association of these factors with AA (no balding versus other) by logistic regression. To investigate whether effects differed by potential disease aggressiveness, we analyzed men with moderate-grade (Gleason scores 57) and high-grade (Gleason scores 810) tumors separately. We also examined the effects in two age groups (i.e., reference age <60 versus 6069). Tests for heterogeneity in the ORs between high- and moderate-grade prostate cancer were performed using polytomous logistic regression models (21) .
| Results |
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Because the electoral roll is never completely up to date, we considered that a more appropriate response rate in controls excluded those who had moved or died, which was 50%. After excluding subjects with missing data on AA and the variables to be controlled for in the analysis, there were 1446 cases (1088 with moderate-grade and 358 with high-grade tumors) and 1390 controls available.
The distributions of demographic variables are shown in Table 1
. The cases were more likely than the controls to be Australian born (OR, 1.38; 95% CI, 1.171.63) and to have at least one first-degree relative affected with prostate cancer (OR, 3.21; 95% CI, 2.454.23). There was no association between AA and educational status, smoking status, or migrant status in either cases or controls (all P > 0.1). Models that excluded those born overseas produced very similar findings (data not shown).
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| Discussion |
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Our observation of an increased risk of prostate cancer associated with vertex baldness is consistent with two small case-control studies (13)
and one cohort study (14)
but not with another cohort study (15)
and two hospital-based case-control studies (16
, 17)
. Of those studies not in agreement with ours, the cohort study of Harvard alumni (15)
assessed mens baldness from photographs taken from college yearbooks published 25 years after graduation when former students were in their mid-forties and compared the men who had died from prostate cancer with those who had not. No attempt was made to assess vertex baldness. A hospital-based case-control study (17)
conducted in Athens, Greece, on 320 prostate cancer patients and a mix of 246 patients without prostate cancer excluded men with benign prostatic hypertrophy from the controls. This could be problematic, given that AA may be associated with benign prostatic hypertrophy (22)
and both are related to 5
R activity (23
, 24)
.
Of the case-control studies in agreement with ours (13) , one was a hospital-based study of 78 cases and 71 controls and the other was a community-based study of 56 cases and 74 controls (13) . The Hamilton-Norwood scale was used to measure AA (19) ; subjects were asked to choose pictures that best described their hair pattern at 30 and 40 years of age. The analysis produced consistent but statistically not significant results: an OR for vertex baldness of 2.44 (95% CI, 0.5710.46); an OR for baldness by age 30 of 2.11 (95% CI, 0.666.73); and an OR for baldness by age 40 of 1.37 (95% CI, 0.474.06). A follow-up of the first National Health and Nutrition Examination Survey, comparing 214 prostate cancer cases with the remaining 4421 men examined for AA at baseline when 2575 years of age, found an OR of 1.5 (95% CI, 1.122.00) for any form of baldness (14) . This estimate has been considered to be possibly attenuated, not only by the lack of specificity of the baldness measurement (they were not able to distinguish vertex baldness) but also by the wide range of ages at which baldness was assessed (25) . It is possible that any association with baldness may be stronger in men who become bald at an early age.
A mechanism for the putative relationship between AA and prostate cancer risk is yet to be established. Because both AA and prostate cancer are androgen dependent, differences in androgen metabolism, coactivators of the AR, AR gene mutations and polymorphisms of the AR, and 5
R genes are all obvious candidates for investigation (26, 27, 28)
. Other candidates for investigation include physiological pathways important to prostate cell differentiation and proliferation, e.g., IGF-1 and the VDR. IGF-1 can lead to aberrant activation of the AR and mediates the perpetuating effects of growth hormone on AA (29)
. Vitamin D (as 1
,25-hydroxyvitamin D) inhibits prostate cell growth (30)
, and polymorphic variation in the VDR has been linked to prostate cancer risk (31)
. 1
,25-Hydroxyvitamin D resistance has been linked to alopecia in humans (32)
, and VDR knockout mice also develop alopecia (33)
.
A case-control study of 159 cases and 156 controls found a positive association between free T levels in serum from men with frontal or vertex baldness, compared with men who had only minimal hair loss (16) . The association between T (and IGF-1) and AA was also found in a cross-sectional study (34) . Associations between prostate cancer and elevated T have been reported in a case-control (35) and a prospective (36) study. In the latter, elevated T levels in blood sampled before diagnosis were associated with increased risk of prostate cancer, especially advanced disease. Other analyses of this cohort study have shown positive associations between IGF-1 and prostate cancer (37) and also between IGF-1 and vertex baldness (38) .
It is considered that premature AA is related to high levels of androgens generally and to high DHT levels specifically in the frontal scalp (39)
, with 5
R-2 playing a central role in the intrafollicular conversion of T to DHT (2)
. This is supported by the immunohistochemical localization, in cryosections of scalp from men with AA, of 5
R-1 staining within sebaceous glands but not in hair follicles and 5
R-2 staining in the root sheath and the infundibular region of the follicle but not within the dermal papilla or sebaceous glands (40)
. Others have shown that the outer root sheaths of frontal hair follicles have higher levels of AR, 5
R-1, and 5
R-2 and less aromatase than in occipital follicles (41)
, and a higher level of AR has been demonstrated in hair follicles from balding skin compared with nonbalding skin (42)
. Aberrant activation of the AR has been demonstrated in vitro with IGF-1, keratinocyte growth factor, and epidermal growth factor. These agents can directly activate the AR in the absence of androgens and may contribute to the progression of prostate cancer and AA (43
, 44)
. Some consider that prostate cancer risk might be associated with the CAG repeat polymorphism in the AR (11
, 27
, 28)
, although we have been unable to detect such an association in our study (data not shown). However, shorter CAG repeat lengths in the ARmay affect androgen-mediated gene expression in hair follicles and sebaceous glands (45)
. Platz et al. (38)
and Ellis et al. (46)
, in comparing men with early-onset AA and older nonbald men, failed to detect any variation in allele, genotype, or haplotype frequencies in the genes encoding 5
R-1, 5
R-2, and insulin, suggesting that these were not associated with early-onset AA. This is not altogether surprising because whole follicle transplantation experiments have demonstrated that each hair follicle is genetically programmed not only to respond, or not respond, to androgens but also in what manner to respond (47)
. Although the geographical patterning of the hair loss in AA is associated with quantitative differences in androgens and numbers of ARs, these are likely to be secondary phenomena because the hair follicle is able to regulate its own response to androgens by enhancing expression of 5
R and ARs in vitro (48)
. Genetic control of AA may reside with differentiation/morphogen genes, e.g., genes that code for developmental regulator proteins implicated in the sonic hedgehog signaling pathway or its cognate receptor patched (49)
. Notably, these genes also play an important role in oncogenic transformation (50)
.
The extent to which different androgens interact with each other, and with the molecules that produce, transport, activate, receive, and remove them from circulation, is far from completely understood. It is possible that common polymorphisms in genes that encode steroid hormones and their reductases and other relevant molecules, e.g., the genes for IGF (and its receptor), the AR, and aromatase, might influence the etiology of all these conditions. To better understand this complexity, there is an obvious need for larger studies of prostate cancer and AA that include measures of polymorphic variation in an increasing number of candidate genes.
| Acknowledgments |
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| Footnotes |
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1 This study was funded by National Health and Medical Research Council Grant 940394, Tattersalls, and The Whitten Foundation, as well as infrastructure provided by the Anti-Cancer Council of Victoria. The contribution of G. S. and P. B. was within the framework of support from the Italian Association of Cancer Research (Associazione Italiana per la Ricerca sul Cancro). ![]()
2 To whom requests for reprints should be addressed, at Cancer Epidemiology Centre, Cancer Control Research Centre, 100 Drummond Street, Carlton South VIC 3053, Australia. ![]()
3 The abbreviations used are: AA, androgenetic alopecia; T, testosterone; IGF, insulin-like growth factor; AR, androgen receptor; DHT, dihydrotestosterone; 5
R, 5-
reductase; PSA, prostate-specific antigen; OR, odds ratio; CI, confidence interval; VDR, vitamin D receptor. ![]()
Received 8/17/01; revised 2/15/02; accepted 3/ 7/02.
| References |
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-reductase isoenzyme expression. J. Clin. Investig., 92: 903-910, 1993.
-reductase deficiency. Am. J. Med., 62: 170-191, 1977.[Medline]
-reductase inhibition in human benign prostatic hyperplasia. Eur. Urol., 37: 367-380, 2000.[Medline]
-reductase gene and its association with prostate cancer: a case-control analysis. Cancer Epidemiol. Biomark. Prev., 6: 189-192, 1997.[Abstract]
-reductase. Cancer Res., 57: 1020-1022, 1997.
-reductase genes. J. Investig. Dermatol., 110: 849-853, 1998.[Medline]
-reductase in human scalp. Br. J. Dermatol., 141: 481-491, 1999.[Medline]
-reductase type I and II, aromatase, and androgen receptor in hair follicles of women and men with androgenic alopecia. J. Investig. Dermatol., 109: 296-300, 1997.[Medline]
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