Pembrolizumab is a systemic treatment option for adult and pediatric patients with unresectable or metastatic, microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) solid tumors...NCCN recommends this treatment only for patients with MSI-H/dMMR or tTMB-high chondrosarcomas, chordomas, Ewing sarcomas, and osteosarcoma.

KEYTRUDA is a programmed death receptor-1 (PD-1)-blocking antibody indicated:...for the treatment of adult and pediatric patients with unresectable or metastatic tumor mutational burden-high (TMB-H) [≥10 mutations/megabase (mut/Mb)] solid tumors, as determined by an FDA-approved test, that have progressed following prior treatment and who have no satisfactory alternative treatment options.

...a case of osteosarcoma treated with sequential chemotherapy and immunotherapy and showed promising therapeutic potential….subsequent long-term immunotherapy (pembrolizumab) maintained continuous remission for 33 months....sequential chemotherapy and maintenance immunotherapy was shown to have good response for the first time on osteosarcoma patient who had high TMB tumor lesions and good tolerance for chemotherapy and immunotherapy.