Phase II Trial of Allogeneic Transplantation Plus Novel Drugs in Multiple Myeloma: Effect of Intensifying Reduced-Intensity Conditioning with Bortezomib and Adding Maintenance Treatment

The use of reduced-intensity conditioning (RIC) regimens has decreased the risk of nonrelapse mortality (NRM) after allogeneic stem cell transplantation (alloSCT). In contrast, disease relapse remains the most frequent cause of treatment failure and death. Owing to both their antimyeloma effect and immunomodulatory properties, novel drugs could improve outcomes after alloSCT. This phase II European Myeloma Network trial was designed to evaluate the combination of alloSCT with novel agents. The study was conducted to evaluate the toxicity and efficacy of RIC intensified with bortezomib (Bz) prior to alloSCT for high-risk (HR) multiple myeloma (MM) patients, as well as the efficacy of post-transplantation maintenance with Bz and lenalidomide (Len). Patients received RIC with Bz on days -9 and -2, fludarabine on days -6 to -4, and melphalan on day -3. Patients who were in complete response (CR) or near CR at day +100 post-transplantation received 6 cycles of Bz every 56 days, and the remaining received Bz, Len, and dexamethasone. Len maintenance was started on day +180 at a dose of 5 mg and continued until relapse or toxicity occurred. Of the 24 patients included, 21 were evaluable on day +100, including 12 in CR, 4 in very good partial response, 3 in partial response, and 2 with relapse or progression. The cumulative incidence (CuI) of relapse was 13.6% (95% confidence interval [CI], 3.2% to 31.3%) at 1 year and 28.5% (95% CI, 11.1% to 48.9%) at 2 years. The CuI of NRM was 21.1% (95% CI, 7.4% to 39.4%) at 2 years. With a median follow-up of 39 months (range, 1 to 67 months), the median event-free survival (EFS) was 29 months, and median overall survival (OS) was not reached. EFS and OS at 3 years were 42.5% (95% CI, 21.9% to 61.7%) and 74.01% (95% CI, 50.9% to 87.5%), respectively. The use of Bz within an RIC regimen allows for a high response rate after alloSCT. Maintenance with Bz and Len is feasible and provides remarkable results in terms of EFS and OS in HR MM patients.