Extraocular sebaceous carcinoma of the lateral neck: Molecular exclusion of Muir-Torre syndrome and management of sporadic Stage III Disease

Extraocular sebaceous carcinoma (SC) is a rare and aggressive adnexal malignancy that may mimic other cutaneous cancers and can be associated with Muir-Torre syndrome, creating diagnostic and management challenges. A 72-year-old man presented with an 18-month history of a slowly-growing, intermittently ulcerated, non-tender left lateral neck nodule associated with occasional bleeding. Imaging demonstrated a vascularized neck lesion with suspicious left cervical lymphadenopathy, while dermoscopy suggested an adnexal tumor. 
Punch biopsy showed an infiltrative dermal neoplasm with sebaceous differentiation, pagetoid spread, and perineural invasion. Immunohistochemistry (IHC) demonstrated diffuse positivity for androgen receptor, EMA, p63, and adipophilin, confirming the diagnosis of sebaceous carcinoma, whereas S100 and HMB-45 were negative. The tumor was staged as pT2N1M0 (stage III). Molecular testing showed microsatellite stability, excluding Lynch/Muir-Torre syndrome and supporting a sporadic etiology related to chronic ultraviolet (UV) exposure.
The patient underwent Mohs micrographic surgery with sentinel lymph node biopsy and selective neck dissection, followed by adjuvant external beam radiotherapy because of nodal involvement and perineural invasion. At 18 months of follow-up, he remained disease-free, with no evidence of local recurrence or distant metastasis. This case highlights the importance of histopathologic, IHC, and molecular evaluation in distinguishing sporadic extraocular sebaceous carcinoma from hereditary syndromic disease and guiding multidisciplinary management.