Phase I dose escalation study of high dose carfilzomib monotherapy for Japanese patients with relapsed or refractory multiple myeloma

We conducted a multicenter, open-label Phase I study of single-agent carfilzomib in Japanese patients with relapsed or refractory multiple myeloma. The primary endpoints were tolerability and safety. Carfilzomib was administrated for 30 min on days 1, 2, 8, 9, 15, and 16 of a 28-day cycle. In cycle 1, doses for days 1 and 2 were 20 mg/m(2), followed by 45 or 56 mg/m(2). Three and four subjects were enrolled in the 20/45 mg/m(2) cohort and 20/56 mg/m(2) cohort. No dose-limiting toxicity was observed, and the tolerability of carfilzomib was confirmed. Pyrexia, hypertension, nausea and vomiting were considered as noteworthy adverse events (AE) when carfilzomib was administered at high doses. Moreover, pyrexia, blood creatinine increased, and body weight gain were observed as acute dose effects. These findings suggest that addition of dexamethasone is important to alleviate acute dose effect. The overall response rates of the 20/45 mg/m(2) and 20/56 mg/m(2) cohort were 66.7 % (two out of three) and 50 % (two out of four), respectively. Carfilzomib administrated at up to 20/56 mg/m(2) was well tolerated and seemed active in Japanese patients with relapsed or refractory multiple myeloma. Clinical Trial Registration: JapicCTI-122020.