Characteristics of finasteride users in comparison with nonusers: A Nordic nationwide study based on individual-level data from Denmark, Finland, and Sweden.

PURPOSE: Published epidemiological studies on the association between finasteride use and the risk of male breast cancer have been inconclusive due to methodological limitations including a few male breast cancer cases included. Determinants of male breast cancer have been studied, but it remains unexplored whether these are also related to finasteride use and thereby constitute potential confounders. This study aimed to assess whether there are differences between finasteride users and nonusers with regard to numerous potential confounders. METHODS: In total, 246 508 finasteride users (≥35 years) were identified in the prescription registries of Denmark (1995-2014), Finland (1997-2013), and Sweden (2005-2014). An equal number of nonusers were sampled. The directed acyclic graph (DAG) methodology was used to identify potential confounders for the association between finasteride and male breast cancer. A logistic regression model compared finasteride users and nonusers with regard to potential confounders that were measurable in registries and population surveys. RESULTS: Finasteride users had higher odds of testicular abnormalities (odds ratio [OR] 1.40; 95% confidence interval [CI] 1.36-1.44), obesity (1.31; 1.23-1.39), exogenous testosterone (1.61; 1.48-1.74), radiation exposure (1.22; 1.18-1.27), and diabetes (1.07; 1.04-1.10) and lower odds of occupational exposure in perfume industry or in high temperature environments (0.93; 0.87-0.99), living alone (0.89; 0.88-0.91), living in urban/suburban areas (0.97; 0.95-0.99), and physical inactivity (0.70; 0.50-0.99) compared to nonusers. CONCLUSIONS: Systematic differences between finasteride users and nonusers were found emphasizing the importance of confounder adjustment of associations between finasteride and male breast cancer.

Finasteride Use and Risk of Male Breast Cancer: A Case-Control Study Using Individual-Level Registry Data from Denmark, Finland, and Sweden.

BACKGROUND: In case reports, concerns have been raised as to whether finasteride use increases the risk of male breast cancer. Previous epidemiologic evidence on the potential link is conflicting. This study aimed to assess whether an association between finasteride use and male breast cancer exists after accounting for potential confounders. METHODS: The source population consisted of all men (≥35 years) from Denmark (1995-2014), Finland (1997-2013), and Sweden (2005-2014). Cases with incident male breast cancer were identified in the cancer registries and matched with 50 density-sampled, age, and country-matched male population controls per case. Exposure information on finasteride use was derived from the prescription registries. Potential confounders were identified using the directed acyclic graph methodology and measured by use of information from nation-wide registries. RESULTS: The study population comprised 1,005 male breast cancer cases and 43,058 controls. Confounder-adjusted odds of finasteride exposure were not statistically significantly increased [OR, 1.09; 95% confidence interval (CI), 0.77-1.54] in breast cancer cases relative to controls. There was no evidence of a dose-response relationship, as the group with greatest exposure to finasteride was associated with lowest OR of male breast cancer [OR, 0.72 (95% CI, 0.40-1.30)]. Sensitivity analyses did not reveal marked changes in results with different exposure definitions or for specific subgroups. CONCLUSIONS: Results from this study provided no evidence that finasteride use was associated with male breast cancer. IMPACT: This large confounder-adjusted study supports the view that exposure to finasteride is not associated materially with male breast cancer risk.

5-alpha Reductase inhibitors and risk of male breast cancer: a systematic review and meta-analysis

Abstract Objective: To assess the relationship between 5α-reductase inhibitors (5ARIs) and the risk of male breast cancer (MBC). Material and Methods: We systematically searched Medline via PubMed, Embase and the Cochrane Library Central Register up to May 2017 to identify published articles related to 5ARIs and the risk of MBC. Results: Summary effect estimates were calculated by a random-effect model, and tests for multivariable-unadjusted pooled risk ratios (RR) and heterogeneity, as well as the sensitivity analyses were conducted to assess publication bias. All four studies were conducted in a quality assessment according to the Newcastle Ottawa Scale system. The strength of association between 5ARIs and the prevalence of MBC was evaluated by using summarized unadjusted pooled RR with a 95% confidence interval [CI]. Four studies involving 595.776 participants, mean age range from 60 to 73.2 years old, were included in a meta-analysis, which produced a summary unadjusted RR of the risk of MBC for the treatment of 5ARIs of 1.16 (95% CI 0.85-1.58, P=0.36) and the multivariable-adjusted RR is 1.03, (95% CI 0.75-1.41, p=0.86). There was no heterogeneity among included studies (I2=0%, P=0.49). Estimates of total effects were generally consistent with the sensitivity. Conclusion: We did not observe a positive association between the use of 5ARIs and MBC. The small number of breast cancer cases exposed to 5ARIs and the lack of an association in our study suggest that the development of breast cancer should not influence the prescribing of 5ARIs therapy.

5-alpha Reductase Inhibitors and risk of male breast cancer: a systematic review and meta-analysis.

OBJECTIVE: To assess the relationship between 5α-reductase inhibitors (5ARIs) and the risk of male breast cancer (MBC). MATERIAL AND METHODS: We systematically searched Medline via PubMed, Embase and the Cochrane Library Central Register up to May 2017 to identify published articles related to 5ARIs and the risk of MBC. RESULTS: Summary effect estimates were calculated by a random-effect model, and tests for multivariable-unadjusted pooled risk ratios (RR) and heterogeneity, as well as the sensitivity analyses were conducted to assess publication bias. All four studies were conducted in a quality assessment according to the Newcastle Ottawa Scale system. The strength of association between 5ARIs and the prevalence of MBC was evaluated by using summarized unadjusted pooled RR with a 95% confidence interval [CI]. Four studies involving 595.776 participants, mean age range from 60 to 73.2 years old, were included in a meta-analysis, which produced a summary unadjusted RR of the risk of MBC for the treatment of 5ARIs of 1.16 (95% CI 0.85-1.58, P=0.36) and the multivariable-adjusted RR is 1.03, (95% CI 0.75-1.41, p=0.86). There was no heterogeneity among included studies (I2=0%, P=0.49). Estimates of total effects were generally consistent with the sensitivity. CONCLUSION: We did not observe a positive association between the use of 5ARIs and MBC. The small number of breast cancer cases exposed to 5ARIs and the lack of na association in our study suggest that the development of breast cancer should not influence the prescribing of 5ARIs therapy.

Occupational exposure to organic solvents and risk of male breast cancer: a European multicenter case-control study.

Objectives The etiology of male breast cancer (MBC) is largely unknown but a causal role of exposure to organic solvents has been suggested. Previous studies on occupational risk factors of breast cancer were often restricted to women who are frequently exposed to lower levels and at a lower frequency than men. We investigated the association between MBC and occupational exposure to petroleum and oxygenated and chlorinated solvents in a multicenter case-control study of rare cancers in Europe. Methods The study included 104 MBC cases and 1901 controls. Detailed lifetime work history was obtained during interviews, together with sociodemographic characteristics, medical history and lifestyle factors. Occupational exposures to solvents were estimated from a job-exposure matrix. Odds ratios (OR) and their 95% confidence intervals (CI) were calculated using unconditional logistic regression models. Results Lifetime cumulative exposure to trichloroethylene >23.9 ppm years was associated with an increased MBC risk, compared to non-exposure [OR (95% CI): 2.1 (1.2-4.0); P trend <0.01). This increase in risk persisted when only exposures that occurred ≥10 years before diagnosis were considered. In addition, a possible role for benzene and ethylene glycol in MBC risk was suggested, but no exposure-response trend was observed. Conclusions These findings add to the evidence of an increased risk of breast cancer among men professionally exposed to trichloroethylene and possibly to benzene or ethylene glycol. Further studies should be conducted in populations with high level of exposure to confirm our results.

Finasteride treatment and male breast cancer: a register-based cohort study in four Nordic countries.

A potential link has been suggested between dispensed finasteride and increased risk of male breast cancer (MBC). Due to the rare occurrence of MBC, it remains to be established if such a relationship exists. The purpose of this study was to combine nationwide registers in four countries to assess the potential association between dispensed finasteride and MBC. A cohort of all males with dispensed finasteride in Denmark, Finland, Norway, and Sweden (1,365,088 person years) was followed up for up to 15 years for breast cancer, and compared to a cohort of males unexposed to finasteride. Individual-level register data included country, dates of dispensed finasteride, MBC diagnosis, and death. Incidence rate ratios (IRRs) were estimated using a generalized linear model with a Poisson distribution. An increased risk of MBC was found among finasteride users (IRR = 1.44, 95% confidence interval [95% CI] = 1.11-1.88) compared to nonusers. The IRR increased to 1.60 (95% CI = 1.20-2.13) when users in Norway and Sweden with short follow-up time were excluded. The highest IRR was seen among men with medium duration of dispensed finasteride, medium accumulated consumption of finasteride, and among men with first dispensed finasteride prescription 1-3 years prior to diagnosis. The analyses suggested possible ascertainment bias and did not support a clear relationship between dispensed finasteride and MBC. In conclusion, a significant association between dispensed finasteride and MBC was identified. However, due to limited data for adjustment of potential confounding and surveillance bias in the present study, further research is needed to confirm these results.

Characterization of mammary adenocarcinomas in male rats after N-methyl-N-nitrosourea exposure--Potential for human male breast cancer model.

The frequency of breast cancer in men is extremely rare, reported to be less than 1% and there is currently no available animal model for male mammary tumors. We compared the characteristics of various immunohistochemical markers in N-methyl-N-nitrosourea (MNU)-induced mammary adenocarcinomas in male and female Crj:CD(SD)IGS rats including: estrogen receptor α (ER), progesterone receptor (PgR), androgen receptor (AR), receptor tyrosine-protein kinase erbB-2 (HER2), GATA binding protein 3 (GATA3), and proliferating cell nuclear antigen (PCNA). Female mammary adenocarcinomas were strongly positive in the nuclei of tumor cells for PCNA and ER (100%) with only 60% and 53% expressing PgR and GATA3, respectively. 100% of male adenocarcinomas also exhibited strongly positive expression in the nuclei of tumor cells for PCNA, with 25% expressing AR and only 8% showing positivity for ER. Male carcinomas did not express PgR or GATA3 and none of the tumors, male or female, were positive for HER2. Based on the observed ER and PgR positivity and HER2 negativity within these tumors, MNU-induced mammary adenocarcinomas in female rats appear to be hormonally dependent, similar to human luminal A type breast cancer. In contrast, MNU-induced mammary adenocarcinomas in male rats showed no reactivity for ER, PgR, HER2 or GATA3, suggesting no hormonal dependency. Both male and female adenocarcinomas showed high proliferating activity by PCNA immunohistochemistry. Based on our literature review, human male breast cancers are mainly dependent on ER and/or PgR, therefore the biological pathogenesis of MNU-induced male mammary cancer in rats may differ from that of male breast cancer in humans.

Evaluation of contaminated drinking water and male breast cancer at Marine Corps Base Camp Lejeune, North Carolina: a case control study.

BACKGROUND: Solvents contaminated drinking water supplies at Marine Corps Base Camp Lejeune during 1950s-1985. METHODS: We conducted a case-control study among Marines to evaluate associations between residential exposure to contaminated drinking water at Camp Lejeune and male breast cancer risk. The study included 71 male breast cancer cases and 373 controls identified from the Department of Veteran's Affairs (VA) cancer registry whose military personnel records were available. Controls were selected from cancers not known to be associated with solvent exposure and included 270 skin cancers, 71 mesotheliomas, and 32 bone cancers. Base assignment and risk factor information came from military personnel and VA records. Groundwater contaminant fate/transport and distribution system models provided monthly estimated residential contaminant levels. We conducted exact logistic regression using the 50th percentile level among exposed controls to create low and high exposure categories. We calculated 95% confidence intervals (CIs) to indicate precision of effect estimates. Exploratory analyses used proportional hazards methods to evaluate associations between exposures and age at diagnosis. RESULTS: After adjusting for age at diagnosis, race, and service in Vietnam, the odds ratio (OR) for ever stationed at Camp Lejeune was 1.14 (95% CI: 0.65, 1.97). Adjusted ORs for high residential cumulative exposures to tetrachloroethylene (PCE), t-1,2 dichloroethylene (DCE), and vinyl chloride were 1.20 [95% CI: 0.16-5.89], 1.50 [95% CI: 0.30-6.11], 1.19 [95% CI: 0.16-5.89], respectively, with a monotonic exposure response relationship for PCE only. However these results were based on two or three cases in the high cumulative exposure categories. Ever stationed at Camp Lejeune and high cumulative exposures to trichloroethylene (TCE), PCE, DCE and vinyl chloride were associated with earlier age at onset for male breast cancer; hazard ratios ranged from 1.4-2.7 with wide confidence intervals for cumulative exposure variables. CONCLUSION: Findings suggested possible associations between male breast cancer and being stationed at Camp Lejeune and cumulative exposure to PCE, DCE, and vinyl chloride. TCE, PCE, DCE and vinyl chloride cumulative exposures showed possible associations with earlier age at onset of male breast cancer. However, this study was limited by small numbers of cases in high exposure categories.

5-α reductase inhibitors, benign prostatic hyperplasia, and risk of male breast cancer.

PURPOSE: 5-α reductase inhibitors (5-ARI) have been suggested to increase the risk of male breast cancer. The aim of this study was to study the risk of breast cancer in men on 5-ARI, in men with benign prostatic hyperplasia (BPH) not on 5-ARI, and in men without BPH. METHODS: We performed a population-based cohort study in Sweden with data from The Prescribed Drug Register, The Patient Register, and The Cancer Register. Men on 5-ARI, men on α-blockers, or men who had undergone a transurethral resection of the prostate (TUR-P) prior to or during 2006-2008 were included as exposed to BPH and a specific treatment thereof. For each exposed man, five unexposed men were selected. Risk of breast cancer was calculated in Cox proportional hazard models. RESULTS: There were 124,183 exposed men and 545,293 unexposed men, and during follow-up (median 6 years), 99 men with breast cancer were diagnosed. Compared to unexposed men, men on 5-ARI had a hazard ratio (HR) of breast cancer of 0.74 (95% confidence interval (CI) 0.27-2.03), men on α-blockers had HR 1.47 (95% CI 0.73-2.95), and men with a TUR-P had HR 1.99 (95% CI 1.05-3.75). CONCLUSION: No increased risk of breast cancer was observed for men on 5-ARI. However, the increased risk of breast cancer among men who had undergone a TUR-P, a strong indicator of BPH, suggests that the endocrine milieu conducive to BPH is associated with male breast cancer.

Breast cancer development in transsexual subjects receiving cross-sex hormone treatment.

INTRODUCTION: Transsexual people receive cross-sex hormones as part of their treatment, potentially inducing hormone-sensitive malignancies. AIM: To examine the occurrence of breast cancer in a large cohort of Dutch male and female transsexual persons, also evaluating whether the epidemiology accords with the natal sex or the new sex. MAIN OUTCOME MEASURE: Number of people with breast cancer between 1975 and 2011. METHODS: We researched the occurrence of breast cancer among transsexual persons 18-80 years with an exposure to cross-sex hormones between 5 to >30 years. Our study included 2,307 male-to-female (MtF) transsexual persons undergoing androgen deprivation and estrogen administration (52,370 person-years of exposure), and 795 female-to-male (FtM) subjects receiving testosterone (15,974 total years of exposure). RESULTS: Among MtF individuals one case was encountered, as well as a probable but not proven second case. The estimated rate of 4.1 per 100,000 person-years (95% confidence interval [CI]: 0.8-13.0) was lower than expected if these two cases are regarded as female breast cancer, but within expectations if viewed as male breast cancer. In FtM subjects, who were younger and had shorter exposure to cross-sex hormones compared with the MtF group, one breast cancer case occurred. This translated into a rate of 5.9 per 100,000 person-years (95% CI: 0.5-27.4), again lower than expected for female breast cancer but within expected norms for male breast cancer. CONCLUSIONS: The number of people studied and duration of hormone exposure are limited but it would appear that cross-sex hormone administration does not increase the risk of breast cancer development, in either MtF or FtM transsexual individuals. Breast carcinoma incidences in both groups are comparable to male breast cancers. Cross-sex hormone treatment of transsexual subjects does not seem to be associated with an increased risk of malignant breast development.

Pleomorphic lobular carcinoma in a male breast: a case report with review of the literature.

Invasive lobular carcinoma (ILC) is a distinct type of breast carcinoma and represents 5-15% of invasive breast carcinomas in female. However, the occurrence of ILC is exceptional in male breast, and the incidence is 1.5-1.9% of male breast carcinomas. Herein, we report a case of pleomorphic lobular carcinoma in a male breast. A 76-year-old Japanese male with a history of treatment with a progestational agent for prostate cancer presented with a right breast tumor. Magnetic resonance imaging showed gynecomastia of bilateral breasts and an irregular-shaped nodule in his right breast. Histopathological study revealed infiltrative neoplastic growth of discohesive tumor cells arranged in single-filed linear cords or trabeculae. These neoplastic cells had variable-sized large nuclei containing occasional nucleoli. Immunohistochemically, these tumor cells lacked E-cadherin expression. Accordingly, an ultimate diagnosis of pleomorphic lobular carcinoma was made. This is the third documented case of pleomorphic lobular carcinoma of male breast. Our analyses of the clinicopathological features of this type of tumor revealed that patients were middle-aged or elderly men, and all cases were free from lymph node metastases or recurrence. Gynecomastia and a history of hormonal agent intake were present only in the current case. The most commonly proposed risk factor for the development of male breast cancer is elevated level of estrogen, and a possible link between the development of male breast cancer and estrogen therapy for prostate cancer has been suggested. The clinicopathological features of ILC of male breast remains unclear; therefore, additional studies are needed to clarify them.

Male breast cancer and 5α-reductase inhibitors finasteride and dutasteride.

PURPOSE: We examined the association between 5α-reductase inhibitors and male breast cancer. MATERIALS AND METHODS: Study participants were men 40 to 85 years old, with prescription and medical coverage, enrolled in the United States IMS LifeLink™ Health Plan claims database between 2001 and 2009. Cases required a primary breast cancer diagnosis (ICD-9-CM 175.x) on 2 different dates and a procedural code for mastectomy or lumpectomy/partial mastectomy with evidence of continuous care (radiation/chemotherapy or diagnoses in 2 or more months). Eligible controls were within 5 years in age and had duration of prior health care enrollment within 6 weeks. Risk set sampling selected 20 controls per case. We assessed the rate ratio for male breast cancer with 5α-reductase inhibitor exposure using conditional logistic regression. Analyses were stratified by duration of health care enrollment before diagnosis (1 year or more, 2 years or more and 3 years or more), each incremental 180 and 365 days of cumulative 5α-reductase inhibitor exposure, and period specific time frames before diagnosis (years 1, 2 and 3). RESULTS: We identified 339 breast cancer cases matched to 6,780 controls. No statistically significant associations were observed between 5α-reductase inhibitors and breast cancer regardless of exposure assessment before the index date (1 year or more-RR 0.70, 95% CI 0.34-1.45; 2 years or more-RR 0.59, 95% CI 0.24-1.48; or 3 years or more-RR 0.75, 95% CI 0.27-2.10). Each subsequent 180 days (RR 1.02, 95% CI 0.67-1.53) and 365 days (RR 1.03, 95% CI 0.45-2.37) of cumulative 5α-reductase inhibitor therapy and period specific rate ratios also showed null associations. CONCLUSIONS: The lack of an association in our study suggests that the development of breast cancer should not influence the prescribing of 5α-reductase inhibitor therapy.

Occupation and occupational exposure to endocrine disrupting chemicals in male breast cancer: a case-control study in Europe.

OBJECTIVES: Male breast cancer is a rare disease of largely unknown aetiology. In addition to genetic and hormone-related risk factors, a large number of environmental chemicals are suspected of playing a role in breast cancer. The identification of occupations or occupational exposures associated with an increased incidence of breast cancer in men may help to identify mammary carcinogens in the environment. METHODS: Occupational risk factors for male breast cancer were investigated in a multi-centre case-control study conducted in eight European countries which included 104 cases and 1901 controls. Lifetime work history was obtained during in-person interviews. Occupational exposures to endocrine disrupting chemicals (alkylphenolic compounds, phthalates, polychlorinated biphenyls and dioxins) were assessed on a case-by-case basis using expert judgement. RESULTS: Male breast cancer incidence was particularly increased in motor vehicle mechanics (OR 2.1, 95% CI 1.0 to 4.4) with a dose-effect relationship with duration of employment. It was also increased in paper makers and painters, forestry and logging workers, health and social workers, and furniture manufacture workers. The OR for exposure to alkylphenolic compounds above the median was 3.8 (95% CI 1.5 to 9.5). This association persisted after adjustment for occupational exposures to other environmental oestrogens. CONCLUSION: These findings suggest that some environmental chemicals are possible mammary carcinogens. Petrol, organic petroleum solvents or polycyclic aromatic hydrocarbons are suspect because of the consistent elevated risk of male breast cancer observed in motor vehicle mechanics. Endocrine disruptors such as alkylphenolic compounds may play a role in breast cancer.

Invasive breast cancer after initiation of testosterone replacement therapy in a man--a warning to endocrinologists.

OBJECTIVE: To alert fellow endocrinologists of a rare side effect of testosterone therapy, for which men with hypogonadism must receive appropriate counseling and monitoring. METHODS: We present clinical features, laboratory data, and histopathologic findings in a man with hypogonadism who received testosterone replacement therapy. RESULTS: A 61-year-old man was referred to an endocrinologist after presenting to his general practitioner with erectile dysfunction and low libido. He had no history of hypothalamic, pituitary, or testicular disorders. There were no other illnesses or medications to account for low testosterone levels. Physical examination was unremarkable. There was no family history of malignant disease. Biochemical investigations confirmed the presence of primary hypogonadism, for which no cause (including Klinefelter syndrome) was identified. Testosterone therapy was initiated to improve sexual function and preserve bone density. Five weeks later, the patient returned to his general practitioner, complaining of a gradually enlarging lump in his right breast. When biopsy showed breast cancer, testosterone therapy was discontinued. Right mastectomy and axillary node clearance were performed. Further histologic examination revealed estrogen receptor-positive, invasive carcinoma, without nodal involvement. The patient remains on tamoxifen therapy and is undergoing follow-up in the breast clinic. After 6 months of treatment, estradiol levels were undetectable, and testosterone levels remained low. CONCLUSION: Although breast cancer has been described in men with hypogonadism receiving long-term testosterone replacement therapy, to our knowledge this is the first report of breast cancer becoming clinically manifest after a short duration (5 weeks) of testosterone treatment. This case should remind clinicians that men receiving testosterone therapy should be warned of the risk of not only prostate cancer but also breast cancer. Patient self-monitoring and breast examinations by the attending physician are recommended.