PDCD1 and colorectal cancer: Overall, this study demonstrated the enhancement of anti-PD-1 antitumor efficacy in a syngeneic mouse model (CT-26 cells in Balb/c) by 5 via upregulating PD-L1 expression as well as angiogenesis inhibition and provided a rationale for the combination of 5 and anti-PD-1 antibody for colorectal cancer treatment in the clinic [61].