PRSS16 and thymoma: The following abnormalities in thymomas could, in theory, contribute to the development of TAMG, but surprisingly are also common in TAMG(−) thymomas [18, 210, 211, 215, 224–226]: the frequently reduced expression of MHCII antigens on TECs; the common MHC haploinsufficiency of TECs due to loss of 6p21; the reduced expression of proteases in cTECs (e.g. PRSS16); the reduced size of medullary compared with cortical areas; the lack of AIRE+ mTECs and of Hassall corpuscles; the defective generation of FOXP3+ Tregs in thymomas; the paucity of B-cells and TMCs (Fig. 4).