Lipid synthesis and processing proteins ABHD5, PGRMC1 and squalene synthase can serve as novel immunohistochemical markers for sebaceous neoplasms and differentiate sebaceous carcinoma from sebaceoma and basal cell carcinoma with clear cell features.

Sebaceous carcinoma represents a rare and potentially fatal adnexal malignancy. Poorly-differentiated sebaceous carcinoma consisting of infiltrative basaloid tumor cells with inapparent lipid vesicles can mimic basal cell carcinoma (BCC). Conversely, other epithelial tumors can exhibit clear cell histopathology and mimic sebaceous carcinoma. At the present time, immunohistochemical markers unique for sebaceous carcinoma are limited. We evaluated the expression of three lipid synthesis/processing protein markers alpha/beta hydrolase domain-containing protein 5 (ABHD5), progesterone receptor membrane component-1 (PGRMC1) and squalene synthase (SQS) in sebaceous carcinoma and investigated their utility in differentiating sebaceous tumors from BCC with clear cell features. Immunohistochemistry was performed on 23 sebaceous carcinomas, 14 sebaceomas and 14 BCCs with clear cell features. In sebaceous carcinomas, ABHD5 showed dispersed, cytoplasmic punctate and/or vesicular staining (n = 19/23, 83%), while PGRMC1 and SQS each showed vesicular and membranous staining in tumor cells (n = 22/23, 96%). In all sebaceomas, these markers highlighted tightly clustered lipid vesicles in sebocytes. All BCCs with clear cell features were negative for these three markers. ABHD5, PGRMC1 and SQS are novel markers for sebaceous carcinoma and can reliably distinguish sebaceous neoplasms from non-sebaceous tumors, specifically BCC with clear cell features.