Expression patterns and prognostic value of programmed death ligand-1 and programmed death 1 in thymoma and thymic carcinoma

Thymic epithelial tumors (TETs) arising in the anterior mediastinum are rare malignancies that account for less than 1% of all adult cancers (1). The incidence of TETs is 1.5 to 3.2 per 1,000,000 person-years (2,3). The International Thymic Malignancy Interest Group database including more than 6,000 patients showed that thymoma and thymic carcinoma accounted for 81% and 14%, respectively, of all TETs (4). Of these, 63%, 23%, and 13% of patients had local (stage I–II), locally advanced (stage III), and disseminated or distant metastatic (stage IV) disease, respectively (4). These figures are consistent with those from population-based studies (2,5).