Abstract Primary central nervous system lymphoma (PCNSL) are rare extranodal large B-cell lymphomas. There are no standard-of-care treatment options for patients with relapsed and refractory PCNSL and the overall prognosis is poor. We conducted a phase 2 clinical trial to evaluate the efficacy and adverse events of PD-1 antibody camrelizumab in relapsed/refractory PCNSL. Enrolled patients received camrelizumab 200mg intravenously every 2 weeks. The primary endpoint was overall response rate (ORR). Here we present results of 20 relapsed PCNSL patients who treated with camrelizumab. Among them,12 were male and 8 were female. The median age was 57 years (range 25-67 years). Fourteen patients were available to evaluate efficacy. After camrelizumab treatment, 4 got complete response (CR), 3 got partial response (PR), 1 got stable disease, and 6 got progressed disease (PD). The ORR was 50%. The median progression-free survival (PFS) was 19.3 weeks (95% CI, 3.1-35.5). 24 week PFS rate was 40%. For the 7 patients who got CR/PR, got a long sustained response, with a median PFS of 93.6 weeks (range 17-211.6+ weeks). One patient developed pseudoprogression 2 months after initiation of treatment. By the last follow-up, 18 patients discontinued treatment (10 PD, 4 complete treatment, 3 withdrawal of informed consent, 1 lost follow-up). Eleven patient got PD. Nine patients received chemotherapy and 5 received radiotherapy after PD. PD-L1 expression, microsatellite stability and mutation burden of the tumors were detected in 9 patients, and all the three factors were not correlated with efficacy. The main drug-related adverse reaction was cutaneous capillary hyperplasia. None of the patients dropped out of the study due to adverse reactions. Our data suggest that camrelizumab is active in relapsed/refractory PCNSL and support further investigation of PD-1 blockade in PCNSL.
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