Antipsychotic-Associated Galactorrhea May Mask Diffuse Ductal Carcinoma in Situ: A Diagnostic Challenge.

Galactorrhea is most often associated with endocrine disorders or drug-induced hyperprolactinemia, particularly from antipsychotics. While commonly benign, persistent or unilateral galactorrhea with abnormal imaging findings warrants careful evaluation to exclude malignancy. We report the case of a 44-year-old woman receiving long-term antipsychotic therapy who developed unilateral (left-predominant) milky nipple discharge compatible with galactorrhea and breast tenderness. Mammography revealed diffusely distributed coarse heterogeneous calcifications, but two ultrasound-guided core needle biopsies (CNB) failed to identify malignancy, showing only papillomas with epithelial hyperplasia and atypia. Due to persistent radiologic suspicion, a tomosynthesis-guided vacuum-assisted biopsy (VAB) was performed and demonstrated low-grade ductal carcinoma in situ (DCIS). Mastectomy confirmed diffuse, multigrade DCIS (low-, intermediate-, and high-grade components), cribriform and comedo type, involving multiple breast quadrants. This case underscores the diagnostic challenges of attributing galactorrhea solely to medication side effects, highlights the limitations of core biopsy in diffuse calcifications, and emphasizes the importance of persistent diagnostic workup when imaging remains suspicious.