Use of novel agents, including proteasome inhibitors and immunomodulatory drugs, has markedly improved outcomes in multiple myeloma (MM) patients. However, most MM patients eventually relapse and require salvage treatments. We report herein the result of a phase I/II study, performed from 2014 to 2017 to assess the feasibility and efficacy of a maximum tolerated dose (MTD) of lenalidomide (Len) combined with a fixed dose of once weekly subcutaneous (sc) 1.3 mg/m2 of bortezomib plus 20 mg of dexamethasone (scVRd regimen) in relapsed/refractory MM patients in the Japanese population. In the phase I part, dose-limiting toxicities were observed in three of six patients treated with 20 mg of Len; the MTD was accordingly defined as 15 mg in our cohort. In the phase II part, the recommended dose of the scVRD regimen showed a 71.4% best overall response rate, with a median overall survival of 14.8 months and a median progression-free survival of 8 months. Severe adverse events (≥ grade 3) were observed in ~ 15% of the patients, indicating the tolerability and efficacy of the regimen. Less prior treatment was associated with higher probability of durable response. This scVRd regimen may thus be a better fit for MM patients in early-stage relapse.
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