PDCD1 and colorectal cancer: In these humanized PD-1/PD-L1 mice implanted with the colorectal cancer cell line MC38, compound A treatment at 10 mg/kg for only 7 days resulted in 60.4% group mean tumor volume reduction (relative to vehicle control) with four out of eight animals exhibiting response similar to those observed in the atezolizumab reference group, including one animal with undetectable tumor at study termination (study day 28; Fig. 3A).