Track: Case Reports

Topic: Neoplasia,Carcinogensis,Tumor Biology

Abstract:

Mixed tumor is an adnexal tumor categorized into apocrine and eccrine types. Apocrine type mixed tumors contain epithelial, myoepithelial, and mesenchymal components, whereas eccrine-type mixed tumors are characterized by ductal elements lined by a single layer of cuboidal cells embedded in predominantly myxoid stroma. Recent studies have identified molecular distinctions between these subtypes: fusion genes involving PLAG1 are found in the apocrine type, and SOX10-internal tandem duplications in the eccrine type. We report a case where a mixed tumor, initially histologically indicative of the eccrine type, was confirmed to be of the apocrine type after demonstrating PLAG positivity via immunohistochemical staining. The patient, a woman in her 70s, had a longstanding subcutaneous mass on her nose. The resected specimen revealed a circumscribed subcutaneous mass with cuboidal cells forming non-branching ductal elements in a myxoid stroma, with no evidence of follicular or sebaceous differentiation. Although initially suspected to be an eccrine type mixed tumor, immunohistochemical positivity for PLAG1 led to the diagnosis of an apocrine type mixed tumor, histologically mimicking the eccrine type. This case highlights the importance of molecular confirmation in distinguishing between apocrine and eccrine mixed tumors

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Rie Yamasaki, M.D., Ph.D.