DP18 Extraocular sebaceous carcinoma in situ

Abstract

Abstract Extraocular sebaceous carcinoma in situ (SCIS) is exceedingly rare with < 10 cases reported in the literature (Jeong KM, Seo JY, Kim A et al. Extraocular sebaceous carcinoma in situ concurrent with actinic keratosis: a case report and review of the literature. Korean J Dermatol 2021; 59:307–9). An 80-year-old man reported a 3-month history of a right forehead lesion that had been bleeding. This was a subtle 5 × 5 mm papule on clinical examination, and dermoscopy showed arborizing telangiectasia. Past medical history was significant for 20 basal cell carcinomas, one squamous cell carcinoma, Bowen disease and actinic keratoses. Histology showed sun-damaged skin with a partially eroded neoplasm of lobular architecture, with surface and infundibular epithelium containing atypical sebocytes and squamous cells with no infiltrative growth pattern, which was consistent with SCIS and was fully excised. Immunohistochemistry revealed patchy adipophilin and androgen receptor staining and stronger epithelial membrane antigen staining. Furthermore, there was preserved expression of MSH2, MSH6, MLH1 and PMS2. Sebaceous carcinoma in situ is a debated entity not formally recognized in the classification of sebaceous neoplasms. Kazakov et al. reported five cases of dermal sebaceous tumours with ‘benign’ architectural features (well-circumscribed and no evidence of invasion) but with cytological atypia (abnormal mitoses and pleomorphism) (Kazakov D, Kutzner H, Spagnolo DV et al. What is extraocular cutaneous sebaceous carcinoma in situ? Am J Dermatopathol 2010; 32:857–8). The authors questioned whether these cases represented sebaceous adenomas with atypia or sebaceous carcinomas (Kazakov et al.). In response, it has been argued that such architectural–cytological discordant tumours can be regarded as SCIS owing to the fact that, by definition, carcinoma in situ is a cancer that remains wholly at the site of origin. However, it is argued that these lesions have an unclear origin and may not arise from sebaceous glands in the skin, unlike the more common aggressive periorbital sebaceous carcinomas that arise from meibomian glands and glands of Zeis (Kazakov et al.). It has been postulated that a SCIS diagnosis should be reserved for intraepidermal tumours not extending beyond the epidermal basement membrane, which is a vanishing minority of sebaceous neoplasms (Kazakov et al.). Similar to our case, a 2021 case report identified SCIS without any connection to an adnexal component but concurrent with actinic keratosis. These authors proposed that the tumour cells of intraepidermal squamous neoplasia can differentiate towards malignant sebocytes (Jeong et al.). Although controversial, SCIS appears to have reasonable, clear histological criteria for diagnosis and an excellent prognosis, with no reports of recurrence following surgical excision. We feel it is important to increase identification to avoid the overtreatment of such lesions.