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Case Reports

Abstract

Malignant adnexal tumors are rare entities that often evade clinical and histopathological recognition. We report a case of a metastatic malignant adnexal tumor with clear cell changes in a 74-year-old immunocompromised female. A 3.5 cm axillary skin lesion was resected, revealing anastomosing cords and nests of polygonal cells with eosinophilic to clear cytoplasm, numerous mitoses, necrosis, and focal epidermoid morphology with pleomorphic and hyperchromatic nuclei. An extensive Immunohistochemical panel favored an adnexal origin over a conventional epithelial primary. Histology closely resembled malignant clear cell hidradenoma (MCCH), though squamous cell carcinoma with clear cell differentiation remained in the differential, particularly given the presence of a lung mass and rarity of MCCH. The combined evidence of immunophenotype, distinctive clear cell morphology, and focal hidradenoma-like areas supported a diagnosis of malignant adnexal tumor. Strong CK positivity in the lung lesion, uncommon for primary pulmonary squamous cell carcinoma, further suggested a distinct origin. Next-generation sequencing of lung, stomach, and skin tissue confirmed a shared molecular profile across all lesions. MCCH is a rare cutaneous adnexal neoplasm. While benign lesions frequently harbor the CRTC1-MAML2 fusion, it is less common in malignant cases, suggesting additional genetic events drive transformation. Sequencing in this case revealed a combination of multiple different mutations. High-grade hidradenocarcinomas demonstrate locally destructive behavior and immunocompromised status may exacerbate aggressiveness. We leverage this case, along with an extensive literature review, to demonstrate how morphology, immunohistochemistry, and molecular tools such as sequencing can be integrated to aid in the accurate distinction of these challenging tumors.