DP02 Understanding the histopathological landscape of sebaceous carcinoma

Abstract Sebaceous carcinoma (SC) is a rare and potentially aggressive cutaneous malignancy. SC is often misdiagnosed clinically, leading to delays in appropriate treatment. Histopathological examination is therefore of utmost importance in differentiating SC from other skin neoplasms. Our aim was to evaluate the quality of histopathological reporting for SC using the Royal College of Pathologists (RCPath) guidelines as standard. We analysed the demographics and histopathological reports of patients with SC between October 2014 and June 2024 in our region across three hospitals. The RCPath guidelines recommends that 95% of reports must include a full set of core data items that includes site of origin, type of specimen, maximum clinical dimension/diameter, overall size of the specimen, diagnostic subtype of adnexal carcinoma, histological grade of tumour differentiation, thickness/depth, level of invasion, lymphovascular invasion, perineural invasion and margins. SC was confirmed with histopathology. Histological features included scalloped nuclei and multilocular cytoplasmic vacuolation indicating sebaceous differentiation, high mitotic activity, necrosis, cellular atypia and intraepithelial spread. Only one report out of 18 (6%) reached the expected standard of 95% for reporting core data items, with a mean compliance of 66%. Major deficiencies were observed in reporting perineural invasion (n = 6, 33%), lymphovascular invasion (n = 6, 33%) and level of invasion (n = 8, 44%). Full compliance (n = 18, 100%) was achieved for site of origin, specimen type, overall specimen size and diagnostic subtype of adnexal carcinoma. The compliance of reporting the remaining core data items was as follows: thickness (n = 10, 56%), maximum clinical dimension/diameter (n = 11, 61%), histological grade of tumour differentiation (n = 12, 67%) and margins (n = 16, 89%). Immunochemistry was performed in 33% (n = 6) of cases, with positive markers including epithelial membrane antigen, adipophilin, androgen receptor, CK7, PRAME, p63, BEREP4, CEA, CD15, CAM5.2 and MOC31. Microsatellite instability (MSI) analysis, which can indicate germline mutations in DNA mismatch repair (MMR) genes responsible for Muir–Torre syndrome, was performed in eight cases (44%), with MSI detected in six (75%). Immunohistochemical examination with respect to an MMR defect could be considered for the diagnosis of SC. This was detected in two cases, both suggesting genetic mutations of the MSH2 gene. This audit revealed significant gaps in the histopathological reporting of SC compared with the RCPath guidelines. Standardized reporting is crucial for accurate diagnosis, management and prognosis. Improving compliance with core data reporting will enhance the quality of pathological information, which in turn enhances clinical decision making.