The MMR-deficient CRC tumors have a remarkably favorable prognosis despite their early onset and rapid progression and respond well to immune checkpoint blockades such as α-PD-1, α-PD-L1, and α-CTLA-4, suggesting that their intrinsic high mutation load could trigger chronic immune surveillance that can be further enhanced by immunotherapy (Le et al, 2015, 2017). Here, CTLA4 is linked to colorectal carcinoma.