Update on sebaceous neoplasia: the morphologic spectrum and molecular genetic drivers of carcinoma

Tumors with sebaceous differentiation represent a challenge to diagnose, classify and occasionally to treat. The histopathologic spectrum of sebaceous neoplasia includes sebaceous adenoma, sebaceoma, and sebaceous carcinoma, while sebaceous hyperplasia represents hyperplasia of benign sebaceous glands surrounding a hair follicle. While often recognizable on morphologic grounds alone, sebaceous lineage also be informed by the application of immunohistochemical studies, including antibodies for adipophilin and Factor XIIIa (AC-1A1 clone). Sebaceous tumors are important to recognize given the relationship to the Muir-Tore autosomal dominant cancer predisposition syndrome. However, although it is well accepted that a sebaceous tumor might exhibit defects in mismatch repair, whether such a defect is related to germline defects in mismatch repair genes (or are due to somatically acquired alterations limited to the tumor cells) remains a critical clinical question with significant implications for the patient. Finally, recently published molecular studies have elaborated a molecular-genetic framework by which to understand the drivers of sebaceous carcinomas arising in different anatomic locations.