Histopathologic Features of Breast Tissue From Transgender Men and Their Associations With Androgen Therapy.

[OBJECTIVES] To assess the histopathologic features of breast tissue of transgender men (TM) undergoing gender-affirming bilateral mastectomies in relation to androgen therapy (AT).

[METHODS] We reviewed 374 transgender bilateral mastectomy cases from 2017 to 2020. Of these, 314 (84.4%) patients received preoperative AT. We compared these with 127 cases of cisgender females undergoing elective breast reduction.

[RESULTS] Breast specimens from TM on AT, compared with cisgender women, showed a median higher gross percentage of fibrous tissue (P < .001), reduced lobular density (P = .004), higher amount of lobular atrophy (P < .001), and lower incidence of cysts (P < .001), apocrine metaplasia (P < .001), calcifications (P < .001), columnar cell change (P = .002), and atypia (P = .003). Each additional month of AT was associated with a 2% decrease in the odds of having nonapocrine cysts (P = .02), a 5% decrease in the odds of having usual ductal hyperplasia (P = .007), and a 0.14% decrease in median lobular density (95% confidence interval, -0.18 to -0.05).

[CONCLUSIONS] In this study, breast specimens from TM, particularly with a history of AT, had a higher proportion of fibrous tissue, fewer lobules, and a higher degree of lobular atrophy than cisgender females. Rare cases of atypia were not predicted by preoperative imaging or gross findings, supporting routine microscopic evaluation of these specimens.