At data cut-off (March 8, 2022), a total of 16 patients (median age: 66.5 years; range: 45-80) completed C17 of cevostamab treatment and were eligible for analysis. Patients had received a median of 6 prior lines of therapy (range: 2-11), with 12 patients having received ≥5 prior therapies. Thirteen patients were triple-class refractory and 11 were penta-refractory. Fifteen patients were refractory to their last prior therapy. Five patients had received prior anti-B-cell maturation antigen (BCMA) targeted therapies, 4 of whom were refractory to anti-BCMA treatment.

Patients received cevostamab target doses ranging from 40-160mg and received a median of 17 cycles of treatment (range: 16-17). Among the 16 patients analyzed, the best overall response (BOR) achieved was: stringent complete response (sCR) in 7 patients, CR in 3 patients, very good partial response (VGPR) in 5 patients, and PR in 1 patient. At data cut-off, 13 of the 16 patients remained in remission, with 8 patients (BOR: 5 sCR, 1 CR, 2 VGPR) maintaining a response ≥6 months after completion of therapy and 3 patients (BOR: 2 sCR, 1 CR) maintaining a response ≥12 months after completion of therapy. Eight patients had <6 months of follow-up. None of the patients (0/10) who completed C17 and attained a sCR or CR had relapsed. Only 3 of the 16 patients (BOR: 2 VGPR, 1 PR) had PD after the completion of C17 of cevostamab. Time to progression following completion of therapy for the 2 patients who achieved a VGPR was 7.8 months and 12.9 months. For the patient who achieved a PR, time to progression was 1.3 months.

Due to its mechanism of action, treatment with cevostamab may be associated with an increased risk of infection. Infections occurred in 2 patients after the completion of C17 of cevostamab therapy. Pneumonia was reported in both patients, with onset after the last dose of 1.3 months and 3.8 months. Both events resolved and both patients have remained on study.