CTLA4 and teratoma: Besides PD-L1 overexpression in GCN, the immune checkpoint cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) is also highly expressed in TILs regardless of the histological TGCT type, while the expression of CTLA-4 in tumor cells is predominantly found in yolk sack tumors, choriocarcinomas, and teratomas [27].