A rare presentation of male breast schwannoma.

Breast schwannomas are rare benign tumors originating from Schwann cells of peripheral nerves. They are exceedingly uncommon in the male breast and are often misdiagnosed as gynecomastia, particularly in patients on prolactin-elevating medications. We report a case of a 40-year-old male with a longstanding palpable mass in the upper outer quadrant of the left chest wall. The patient had a history of schizoaffective disorder and was on antipsychotic therapy, initially leading to the clinical presumption of gynecomastia. Diagnostic mammography revealed a well-circumscribed, noncalcified mass adjacent to the pectoralis muscle. Ultrasound demonstrated a heterogeneously hypoechoic lesion with cystic changes, classified as BI-RADS 4. Ultrasound-guided core biopsy revealed a schwannoma with S100 positivity which was confirmed on final surgical pathology after excision. This case underscores the importance of maintaining a broad differential for male breast masses and highlights the limitations of imaging alone in distinguishing rare benign neoplasms from malignancy. Biopsy remains essential for diagnosis, particularly in patients with confounding clinical risk factors.