Effects of hormones and hormone therapy on breast tissue in transgender patients: a concise review

Purpose Hormone replacement therapy (HRT) has become a mainstay medical treatment option for management of gender dysphoria in transgender patients of both biologic sexes. Very little is known about the long-term effects of steroid hormone modulation on breast tissue in this population. Most of the data available on the effects of HRT on breast and reproductive tissues come from studies of postmenopausal cisgender women. Therapeutic regimens are often provider-dependent, and there, are no uniform guidelines in place for cancer surveillance in transgender patients. In this review, we present what forms of hormone therapy and hormone modulation are available to transgender patients, what is known about their effects on male and female breast tissue, and what other endogenous and exogenous factors contribute to the macroscopic and cellular changes observed. Methods A search for the existing literature focusing on therapeutic regimens and the effects of HRT on breast tissue provided the most current information available for this review. Recent evidence-based reports (since the year 2000) and reviews were given priority over anecdotal evidence and expert opinions when conflicting information was encountered. Older resources were considered when primary sources were needed. Given the paucity of available articles on this subject, all resources were given careful consideration. Results Information about the risks associated with HRT in the current literature and in this setting is limited and often conflicting, due to a scarcity of long-term studies tracking breast pathology among transgender men and women. Conclusions We conclude that the long-term effects of off-label pharmaceutical use for modulation of hormone levels and sexual characteristics in transgender patients have not been well studied. The tendency of steroid hormones to promote the growth of certain cancers also raises questions about the safety of differing doses and drug combinations. Further clinical and laboratory study is needed to better establish safety and dosing guidelines in transgender patients.