Unusual presentation of extra-ocular sebaceous carcinoma mimicking squamous cell carcinoma

Introduction: Sebaceous carcinomas (SC) are rare and aggressive malignancies. Accounting for approximately 0.2–4.6% of all skin cancers, they are considered uncommon. With its diverse clinical presentation, SC frequently resembles other types of skin tumors, posing diagnostic challenges, and immunohistological studies are essential for achieving a definitive diagnosis.
Case report: A 54-year-old female patient, was referred for the management of multiple facial lesions. Clinical examination revealed on the upper right lip an erythematous plaque, confirmed by skin biopsy as a squamous cell carcinoma. The right nasal wing had an ill-defined oval-shaped erythematous-crusty plaque, with polarized dermoscopy showing the presence of chrysalides, erosions, keratin plugs, glomerular and linear vessels surrounded by a whitish halo, suggesting a keratinizing tumor such as squamous cell carcinoma. But histological examination and immunohistochemistry confirmed the diagnosis of sebaceous carcinoma.
Discussion: Sebaceous carcinoma often resembles inflammatory diseases or other tumor types in both clinical and histological aspects, presenting an ongoing challenge for clinicians, surgeons, and pathologists in terms of early detection, accurate diagnosis, and appropriate treatment.
Our case presents a unique manifestation of sebaceous carcinoma, initially clinically appearing as a plaque and also dermoscopically mimicking a squamous cell carcinoma by displaying a dermoscopic pattern reminiscent of a keratinizing tumor. The diagnosis was confirmed through histological examination complemented by immunohistochemistry using strongly positive androgen receptors. The second distinctive aspect is the juxtaposition of both squamous cell carcinoma and sebaceous carcinoma, leading to their excision as a single unit with 6 mm margins, as recommended.