Apocrine variant of intraductal carcinoma of the parotid gland with sebaceous-like differentiation: expanding morphological and molecular spectrum of an enigmatic entity.

Intraductal carcinoma (IDC) is a rare tumor of the salivary glands. Here, we report a unique case of apocrine IDC of the parotid gland of a 60-year-old male, exhibiting a striking sebaceous-like differentiation. Microscopically, the tumor displayed a papillary growth pattern with apocrine cells (AR-positive; S100/SOX10-negative) and distinct areas harboring clear, vacuolated cells resembling sebaceous cells (CK7/S100/SOX10-positive; AR negative). Molecular genetic analysis revealed mutations in AKT1 and BRAF genes. An AKT1 gene mutation has earlier been described in sclerosing polycystic adenoma (SPA), suggesting a possible link between IDC and SPA, while BRAF V600E mutations were reported in an oncocytic subtype of IDC, but not in the apocrine one. Since IDC is an indolent disease, its recognition is a key to prevent unwarranted overtreatment. Further evidence is needed to determine whether apocrine IDC with sebaceous-like differentiation represents a novel morphological variant of the apocrine subtype of IDC or a novel salivary gland entity.