KIT and thymic carcinoma: Thymic carcinomas are histologically characterized by marked cytological atypia, increased mitotic activity, and destruction of the lobular architecture.16) In contrast, thymomas—whether necrotic or not—tend to retain some elements of lobulated structure and exhibit less pronounced atypia.1) Immunohistochemical profiling aids in this differentiation: thymic carcinomas often express CD5 and CD117,16) whereas thymomas generally do not.