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Abstract

Primary cutaneous adenoid cystic carcinoma (PCACC) of the axilla is a rare adnexal malignancy with characteristic histopathologic and immunophenotypic features, whose recognition is essential for accurate diagnosis, origin determination, and surgical management. A 45-year-old female presented with a 5.2 cm superficial left axillary mass, initially suspected to represent breast cancer. Diagnostic mammography and targeted ultrasound demonstrated a vascular dermal-based lesion. An excisional biopsy was performed, with histologic evaluation, margin assessment, and immunohistochemistry (IHC) for epithelial, myoepithelial, and adnexal markers. Histology revealed a dermal and subcutaneous infiltrative neoplasm composed of ducts, cords, and cribriform nests within mucinous and hyalinized stroma, consistent with adenoid cystic carcinoma. Foci of in situ change were present within native apocrine and eccrine ductal structures, supporting primary cutaneous adnexal origin rather than ectopic breast tissue. Perineural invasion was absent, though tumor closely approached vascular structures. Margins were involved (medial, superior) or close (<1 mm). IHC demonstrated diffuse CD117, SOX10, cytokeratin 7, and S100 positivity, with p63 highlighting myoepithelial components; EMA was focally positive luminally. Special stains confirmed mucin within cribriform spaces. This case represents a rare axillary PCACC of apocrine/eccrine origin, confirmed by in situ change in native adnexal structures. While distant metastases are rare, local recurrence is common; complete excision with negative margins is the preferred treatment, with postoperative radiation considered in incompletely excised or high-risk cases. Recognition of the characteristic cribriform architecture, dual cell population, and adnexal ductal involvement is key to distinguishing PCACC from salivary or breast-derived lesions.