In the broader CRC population, including microsatellite-stable (MSS)-CRC, monotherapy with checkpoint inhibitors such as anti-programmed cell death-1 (PD-1) or anti-programmed cell death ligand-1 (PD-L1) antibodies has resulted in limited or no anti-tumour activity [8, 10]. Here, PDCD1 is linked to colorectal carcinoma.