They found that even after standard anti-PD-1 treatment, still some patients with colorectal cancer and melanoma develop resistance, because of insufficient immune response generated by the tumors with low mutation burden issues (mismatch-repair-proficient or microsatellite instability-low ‘pMMR-MSI-L’) constituting ~85% of the patients [159]. Here, PDCD1 is linked to colorectal cancer.