Sebaceous carcinoma is composed of a haphazard mixture of basaloid germinative cells and smaller numbers of more mature-appearing sebaceous cells in irregular lobular, trabecular, or diffuse sheet-like growth patterns. The basaloid cells have round or oval vesicular nuclei, punctate nucleoli and brisk mitotic activity. Comedonecrosis is often present. There may be perineural and lymphatic/vascular invasion. Poorly-differentiated cases are composed almost entirely of pleomorphic basaloid cells and have only rare foci of lipid-containing differentiated sebaceous cells. Some cases show prominent keratinization which may lead to diagnostic confusion with squamous cell carcinoma.