Immune checkpoint blockade using antibodies that interfere with binding of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) to CD80 and CD86, or with binding of PD-1 to PD-L1 and PD-L2, are the first therapies directed against the TME that have been effective at achieving meaningful cancer control. This evidence concerns the gene CTLA4 and cancer.