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Case ReportsAbstract
Sebaceous carcinoma is a rare, aggressive malignancy most commonly found in the periocular region. Extraocular presentations are less frequent and may mimic or coexist with other cutaneous neoplasms, making diagnosis challenging. An 86-year-old male presented with a 2-year history of an enlarging, intermittently bleeding plaque on the right frontal scalp. He denied routine dermatologic evaluations. Physical examination revealed a 3.5 × 2.5 cm verrucous, heme-crusted plaque. Shave biopsy revealed poorly differentiated carcinoma with basaloid features, clear cell change, and “monster cells.” Immunohistochemistry demonstrated positivity for CK5/6, AE1/AE3 (partial), EMA, and p63. Ber-EP4, Sox10, Melan-A, CD31, CK20, and neuroendocrine markers were negative. Adipophilin staining was positive in a membranous pattern within the dermal component, but negative in the epidermis, supporting the diagnosis of coexisting sebaceous carcinoma and Bowen’s disease. The patient underwent Mohs micrographic surgery with full-thickness skin graft (FTSG) reconstruction. Tumor board review noted high-risk features including perineural invasion and deep extension, although the second Mohs layer was clear. CT neck imaging showed no evidence of nodal involvement or metastasis. Given the absence of gross extension and the radioresistant nature of sebaceous carcinoma, adjuvant radiation therapy was not recommended. This case highlights the rare coexistence of extraocular sebaceous carcinoma with squamous cell carcinoma in situ. Accurate diagnosis required careful histopathologic evaluation and immunohistochemical staining, particularly adipophilin, which played a critical role in distinguishing sebaceous differentiation. Recognition of such hybrid lesions is essential for guiding appropriate surgical and oncologic management.