NUT Midline Carcinoma Masquerading As a Thymic Carcinoma

Abstract

Thymic carcinomas are rare tumors that arise from the epithelium of the thymus gland and characterized by cytologic atypia, invasiveness, and high risk of relapse and death.1–3 The current WHO schema recognizes at least 11 histologic subtypes.4–7 Undifferentiated thymic carcinoma is one of the subtypes that can be indistinguishable from other poorly differentiated carcinomas such as NUT midline carcinoma (NMC).8 Despite the aggressive nature of both diseases, a correct diagnosis is important because of the recent development of targeted therapies for NMCs. Herein we describe two cases of a particularly aggressive form of disease and discuss the differential diagnosis of these lesions.