P031 Insights on sebaceous carcinoma: a decade in review

Abstract Sebaceous carcinoma (SC) is an uncommon but potentially aggressive cutaneous malignancy. It is classified by anatomical location as ocular or extraocular. It is the most common malignant adnexal tumour of the skin in the head and neck region. We retrospectively analysed the demographics, risk factors, investigations and outcomes for patients with SC in our region between October 2014 and June 2024. Eighteen patients with SC were identified from the pathology database across three hospitals. The median age at diagnosis was 77 years (range 50–91) and there was a male preponderance (12 men and six women). The majority of SCs were extraocular (n = 14, 78%) and presented on the head and neck (n = 13, 72%), where sebaceous gland concentration is the highest. Older age (defined as ≥ 60 years) was the major risk factor for SC development (n = 16, 89%). Immunosuppression was identified in five (28%) patients, five were on long-term immunosuppressive medications and eight (44%) had associated malignancies including cancer of the bladder, bowel, pleura, prostate and lung and haemato-oncological disease. The most common prehistology diagnosis was squamous cell carcinoma (n = 10, 43%), followed by basal cell carcinoma (n = 4, 17%). SC was not listed in any of the clinical differentials, confirming that it is often misdiagnosed due to its rarity and variable clinical presentation. Two patients (11%) met the criteria for Muir–Torre syndrome (MTS) according to the Mayo principles, with one having confirmed MTS (Lynch syndrome). Analysis of microsatellite instability (MSI), which can reveal germline mutations in the DNA mismatch repair (MMR) genes that cause MTS, was carried out in eight patients (44%), and MSI was found in six (75%). Two cases were identified by immunohistochemical analysis in relation to an MMR defect, both suggesting genetic mutations of the MSH2 gene. Histopathology confirmed sebaceous differentiation with various degrees of differentiation and atypia supported by an immunohistochemical panel used in six patients (33%). All SCs were completely removed surgically, with two undergoing wide local excision with a margin of 5 mm. The median follow-up was 26 months (range 2–66) and no recurrences or metastases have been identified to date. Eight patients (44%) died during follow-up, with causes of death being multifactorial. In conclusion, the results of our case series highlight the rarity and nonspecific presentation of SC. High clinical suspicion is necessary to avoid diagnostic and therapeutic delays. Our results confirm the higher incidence of SC in male patients and older patients, and at extraocular sites. Elevated risk for the development of SC has been identified with underlying immunosuppression, as seen in similar studies. Histopathological examination remains crucial for accurate diagnosis and management.