A Case of Squamous Cell Carcinoma of the Breast with Low-Grade Adenosquamous Carcinoma.

A 68-year-old woman with a breast mass was referred to our hospital. Imaging studies showed an oval well-defined mass, 1.3 cm in size, in her left lower outer quadrant of the breast. Core needle biopsy with immunohistochemical staining showed atypical spindle cells forming solid nests with necrosis and papillary lesions, leading to the tentative and pre-operative diagnosis of invasive ductal carcinoma. Due to the absence of daughter nodules, extensive ductal spread, and lymphadenopathy on imaging evaluation, the patient underwent breast-conserving surgery and sentinel node biopsy, resulting in negative surgical margins and no lymph node involvement. Post-operative pathological examination showed triple negative atypical cells with squamous differentiation, squamous cell carcinoma (SCC), with cystic parts and a small amount of low-grade adenosquamous cell carcinoma (LGASC), both encompassing the cystic parts in a contiguous fashion. No cases with synchronous SCC and LGASC in the breast have been reported to date. An etiologic correlation between SCC and LGASC should be further evaluated.