PDCD1 and neoplasm: In microsatellite unstable endometrial cancer, due to mutations in DNA polymerase epsilon (POLE) there is a higher number of CD3+ and CD8+ tumour-infiltrating lymphocytes (TILs), as well as increased PD-1 expression on TILs compared with microsatellite stable tumours, possibly due to increased antigenicity (Howitt et al, 2015).