Extraocular cutaneous sebaceous carcinoma in a patient with Muir-Torre syndrome: special emphasis on histologic and dermoscopic features.

Cutaneous sebaceous carcinoma (CSC) can be classified into periocular and extraocular and can occur as part of Muir-Torre syndrome. It is usually a pink-red or yellow solitary nodule, mainly located in the head and neck region. According to the literature, dermoscopy is characterized in most cases by a yellow color, polymorphic vessels, and ulceration. We performed a review of the literature, and we found 14 papers describing the dermoscopic features of 33 sebaceous carcinomas, to which we added a case that we have recently observed. Compared to the data of the literature and in particular to the latest published reviews, we found that milky-red areas are frequently observed in CSC (47% of the cases) and can be added to the main dermoscopic features for the diagnosis. In our case, histology showed some features that were consistent with a CSC with a secretory pattern, and other features that were instead consistent with a non-secretory pattern. This was probably due to the fact that the lesion we observed was a moderately differentiated and not well-differentiated CSC. The presence of a CSC should always alert the clinician to the possible association with Muir-Torre syndrome, and immunohistochemistry for mismatch repair gene defects can help in the diagnostic pathway.