Nuclear factor XIIIa staining (clone AC-1A1 mouse monoclonal) is a highly sensitive marker of sebaceous differentiation in normal and neoplastic sebocytes

Background Sebaceous proliferations are common and may be confused with other cutaneous neoplasms. Few useful or specific immunohistochemical markers for sebaceous differentiation are available. We incidentally observed strong factor XIIIa (Ventana clone AC-1A1 on Ventana Benchmark Ultra stainer) nuclear staining in normal sebaceous glands and hypothesized that this might be a useful marker in sebaceous proliferations. Methods Immunohistochemistry for factor XIIIa (AC-1A1) was performed on seven sebaceous hyperplasias, eight sebaceous adenomas, five sebaceomas, seven sebaceous carcinomas. Results Strong nuclear factor XIIIa (AC-1A1) staining was present in 100% of normal sebaceous glands, 100% of sebaceous hyperplasia, adenoma and carcinoma, and 80% of sebaceoma. Moderately or poorly differentiated squamous cell carcinomas (SCCs) (n = 26) were also stained for factor XIIIa (AC-1A1); two showed focal strong staining (8%), but the remainder showed only weak or negative staining (92%). In contrast, factor XIIIa clones from Abcam, Cambridge, MA, USA (EP3372) and Vector Laboratories, Burlingame, CA, USA (E980.1) were negative in sebocyte nuclei. Conclusions We report the novel finding of consistent nuclear factor XIIIa (AC-1A1) staining in normal, hyperplastic and neoplastic sebocytes. Factor XIIIa (AC-1A1) is a highly sensitive marker of sebaceous differentiation. It may have potential clinical utility as a specific marker to distinguish sebaceous carcinoma from poorly differentiated SCC.