PDCD1 and neoplasm: Notably, combining TTFields with an inhibitor of programmed cell death protein 1 (PD-1) reduced the tumour volume in lung- and colon-tumour-bearing mice compared with sham control and compared with mice treated with TTFields or the inhibitor alone,89 suggesting that PD-1 inhibition might further promote the antitumour immune response elicited by TTFields treatment.