Safety, efficacy, and pharmacokinetics (PK) of daratumumab as a monotherapy were investigated in Japanese patients with relapsed/refractory multiple myeloma (MM). This multicenter, dose-escalation study included patients (age ≥20 years) with ≥2 prior therapies. Daratumumab was administered intravenously: 8 mg/kg (n = 4) and 16 mg/kg (n = 5). The primary endpoint was safety. Secondary endpoints included objective response, overall response rate (ORR), progression-free survival (PFS), PK, and immunogenicity. Daratumumab was well-tolerated. Eight patients experienced Grade ≥3 adverse event (AE). Four serious AEs were observed in three patients; no AEs leading to death. Infusion-related reactions occurred in four (44%) patients and were Grade 1 or 2. Mean (SD) cumulative dose of daratumumab was 132.3 (108.5) mg/kg. Median duration of follow-up was 10.5 months (range 2.3, 16.4) for 8 mg/kg cohort and 9.9 months (range 1.7, 13.2) for 16 mg/kg cohort. The ORR (44%) comprised 1 and 3 partial responses in 8 and 16 mg/kg cohorts, respectively. The median PFS was 6 months for 8 mg/kg cohort, 9.5 months for 16 mg/kg cohort. Daratumumab serum exposure was increased with increasing dose. Antibodies against daratumumab were not observed. Daratumumab was safe and well-tolerated in Japanese patients with relapsed /refractory MM.
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