CTLA4 and cancer: These factors can be produced by the immune cells of the tumor microenvironment or the cancer cells; by releasing substances such as TGF-beta, IL-10, or prostaglandin E2 into the extracellular matrix, as well as by membrane expression of molecules such as CTLA-4, PD-L1, or PD-L2, they create an immunosuppressive environment in the tumor [6,24].