Apocrine ductal carcinoma in situ associated with testosterone therapy in a transgender individual

We report the first case of apocrine ductal carcinoma in situ (DCIS) in a female-to-male transgender individual on testosterone therapy (TT). The gender confirmation total mastectomy revealed 2 cm DCIS with apocrine cytology, high nuclear grade with associated calcification, and necrosis. Immunohistochemistry revealed the DCIS was negative for ER, positive for AR with HER2/neu overexpression (3+). This patient with negative screening mammography developed apocrine DCIS on TT, suggesting that gender-affirming hormone therapy may have advanced malignant transformation of atypical apocrine cells. This may have implications for increased surveillance within the transgender population.