Male Breast Cancer

Breast cancer in men is very rare. It is estimated that about 1,500 men will develop breast cancer, and 400 will die from the disease this year. The lifetime risk of being diagnosed with male breast cancer is 0.11% (about 1 in 1000) compared with 13.0% (about 130 in 1000) in women. Because male breast cancer is so rare, men in the general population do not undergo breast cancer screening with mammography and clinical breast examinations. Therefore, breast cancer is often detected when men present to their health care providers with a painless firm breast mass.

Risk Factors

The cause of breast cancer in men is poorly understood. The majority of breast cancers in men and women have no known risk factors. It is believed that disorders which cause male sex hormone imbalances or increased estrogen production may play an important role in male breast cancer development. The genetic syndrome, Kleinfelter’s disease, which affects 1 in every 1000 men, is responsible for about 3-8% of male breast cancer cases. Men born with this disease have an extra X chromosome, low testosterone levels, small testes and poor development of male sexual characteristics. Gynecomastia, an excessive development of the male mammary glands, may be caused by an overproduction of estrogen and may be associated with an increased risk of developing male breast cancer. Other less common causes of male breast cancer include radiation exposure, liver disease, obesity and exposure to estrogen medication².

Having a family history of breast cancer also contributes to male breast cancer risk. The chance of developing breast cancer is twice as high in men who have sisters and mothers affected with breast cancer. A high proportion (approximately 17%) of men with breast cancer selected from the general U.S population have a mother or sister with breast or ovarian cancer³.

The contribution of mutations in the breast cancer predisposition genes BRCA1 and BRCA2 to inherited male breast cancer has been investigated. In a selected study of 237 families with ovarian and breast cancer, the majority of families (76%) that had both men and women affected with breast cancer had a mutation in the BRCA2 gene. Families that had breast and ovarian cancer without male breast cancers were more likely to have mutations in the BRCA1 gene⁴.In the general population, however, only 4% of families with a man who has breast cancer have a mutation in BRCA2⁵.Among men who are carriers of a mutation in the BRCA2 gene, the lifetime risk of developing breast cancer is increased to 6%.This means that if 100 men who are BRCA2 mutations carriers live until age 70, six will develop an invasive breast cancer².Because of this increased risk of developing cancer, it is recommended that men with BRCA2 mutations receive annual mammograms and frequent clinical breast examinations. Increasing public awareness about male breast cancer is important to increase the early diagnosis of breast cancer in men. In addition, the diagnosis of breast cancer in a man may have important consequences for other family members at risk for developing the disease.

References

1. R Greenlee, M Hill-Harmon, T Murray. Cancer statistics, 2001. CA Cancer J Clin. 51;15-36, 2001

2. H Lynch, P. Watson, S Narod. The genetic epidemiology of male breast cancer. Cancer 86; 744-746, 1999

3. K Rosenblatt, D. Thomas, A McTiernan et al. Breast cancer in men. Aspects of familial aggregation. JNCI 83:849-854, 1991

4. D. Ford, DF Easton, M Statton et al. Genetic heterogeneity and penetrance analysis of the BRCA1 and BRCA2 genes in Breast Cancer Families. Am J Hum Genet 62; 676-689, 1998

5. L Friedman, S. Gayther, T Kurosake et al. Mutation analysis of BRCA1 and BRCA2 in a male breast cancer population. Am J Hum Genet 60; 313-319, 1997

Abenaa M Brewster MD, MHS