Adenoid Cystic Carcinoma of the Male Breast: An Exceptionally Rare Presentation.

Background: Adenoid cystic carcinoma (ACC) of the breast is an exceedingly rare malignancy, accounting for less than 0.1% of all breast cancers. It typically affects postmenopausal women and is exceptionally uncommon in men, with fewer than 20 cases reported in the literature. Histologically, ACC is a biphasic tumor composed of epithelial and myoepithelial cells with distinct cribriform, tubular, and solid-basaloid subtypes. Awareness of this condition in men is essential to prevent misdiagnosis and guide appropriate management. Case Presentation: We report the case of a 40-year-old man who presented with a painful right breast mass that had been present for 3 years. Ultrasonography revealed multiple solid lesions, and histopathological examination following surgical excision confirmed ACC with cribriform and solid patterns. Immunohistochemistry results were negative for ER, PR, HER2, and p53, with a Ki-67 index of 17%. Although a chest CT scan revealed suspicious bilateral pulmonary nodules, FDG-PET/CT did not reveal evidence of distant metastasis. Subsequent total mastectomy after 3 months revealed cribriform ACC without lymph node involvement. Due to imaging findings suggestive of possible local recurrence or residual disease, the patient was treated with adjuvant radiotherapy. Conclusion: This case highlights the importance of considering ACC in the differential diagnosis of breast masses in male patients. Given the rarity of this tumor in males, accurate histopathological and immunohistochemical diagnoses are critical to avoid misclassification. Although the overall prognosis is favorable, close follow-up is warranted because of the potential for recurrence and metastases.