PDCD1LG2 and osteosarcoma: Elevated expression of PD-L2 has been reported in human reproductive cancers,46 oesophageal carcinomas,47 some soft tissue sarcomas,48 osteosarcoma,49 among others, and it is associated with tumour cell survival, migration, and resistance to chemotherapy.22,48,50,51 PD-L2 does not require a conformational change to bind PD-1, as does PD-L1, with a higher affinity for PD-1 than PD-L1.52 Yet, PD-L2 has been less thoroughly investigated than has PD-L1, on which the majority of the published findings are focused.