Basaloid‐Solid Adenoid Cystic Carcinoma of the Breast: A Case Report and Literature Review

Solid-basaloid adenoid cystic carcinoma (SB-AdCC) of the breast is a rare neoplasm. We report the case of a 78-year-old woman who presented with a progressively enlarging right breast mass over 3 years. Clinical examination revealed a 6-cm mass with visible skin ulceration and right axillary lymphadenopathy. Imaging suggested malignancy, and biopsy showed a poorly differentiated tumor composed of basaloid cells arranged in solid nests with focal cribriform areas and necrosis. Immunohistochemically, the epithelial cells were positive for CD117 and CK7, whereas the myoepithelial component showed focal positivity for p63, CK5/6, and S100, and the tumor was negative for ER, PR, and HER2, with a Ki-67 index of approximately 40%. These findings supported a diagnosis of SB-AdCC of the breast with nodal metastasis. After multidisciplinary discussion, the patient underwent palliative mastectomy. At 12-month follow-up, local recurrence and bilateral axillary metastases were identified. This case emphasizes the diagnostic challenge of SB-AdCC, its overlap with basaloid carcinoma, and the importance of recognizing its distinct morphological and molecular features.