SIRPA and chordoma: The effects of many immune checkpoints, including LAG3, TIM3, SIRPα, HHLA2, MAGEA4, VISTA and TIGIT [56,57,58,59,60,61,62], have been validated in chordoma, and five of them (TIM3, SIRPα, HHLA2, MAGEA4 and VISTA) were only evaluated in preclinical study.