A case report of a primary infiltrating carcinoma with features of low-grade adenosquamous carcinoma in the axilla of a 51-year-old male patient

Summary: Low grade adenosquamous carcinoma (LGASC) is a tumor of the breast parenchyma in females. Our patient is a 51-year-old male presenting with an enlarging, mildly painful nodule in the right axilla that presented clinically as a subcutaneous cyst with a prominent follicular pore. Histopathologic examination revealed a 1.8 cm neoplastic proliferation of cells within the dermis and subcutaneous tissue. The tumor was in the form of strands and ducts within a desmoplastic stroma with glandular and squamous differentiation. Definitive background breast tissue was not seen. Foci of perineural invasion were present. Immunohistochemical staining revealed positivity for CK7, CEA and EMA which highlighted the prominent duct formation. p63 highlighted variably retained myoepithelial layer surrounding the infiltrative glands/ducts. SMA showed lamellar staining within the desmoplastic stroma around the infiltrative strands. YAP-1 expression was retained. The tumor was negative for GCDFP and NUT. The findings were found to represent a low grade adenosquamous carcinoma. The excision and sentinel lymph nodes were negative for the remaining tumor. Our case is likely cutaneous adnexal origin given the superficial location, axillary location, and lack of definitive background breast glandular tissue. This report is further evidence to consider LGASC in neoplasms of the axilla in male patients.