Ixazomib-Based Induction Followed By Single-Agent Ixazomib Maintenance in Transplant Ineligible, Newly Diagnosed Multiple Myeloma Patients: Updated Results of the EMN10-Unito Trial

INTRODUCTION. The proteasome inhibitor (PI) Ixazomib, approved for the treatment of relapsed/refractory multiple myeloma (MM), represents an appealing option for the management of elderly patients, due to its oral administration and the lack of peripheral neuropathy. We previously presented preliminary results of the phase II EMN10-Unito study investigating Ixazomib in combination with dexamethasone (Id), Cyclophosphamide-dexamethasone (ICd), Thalidomide-dexamethasone (ITd) or Bendamustine-dexamethasone (IBd) as induction therapy followed by single-agent Ixazomib maintenance in transplant-ineligible newly diagnosed (ND) MM patients. Here we present updated results of the study with a longer follow-up.

METHODS. Transplant-ineligible NDMM patients ≥65 years were enrolled. Treatment consisted of 9 28-day induction cycles of Ixazomib 4 mg on days 1,8,15 and dexamethasone 40 mg on days 1,8,15,22 or Id plus either Cyclophosphamide 300 mg/m² orally on days 1,8,15 or Thalidomide 100 mg/day or Bendamustine 75 mg/m² iv on days 1,8; followed by Ixazomib maintenance (4 mg on days 1,8,15) for up to 2 years. The primary endpoint was the selection of the most effective induction regimen considering a 2-year progression-free survival (PFS) ≥65% as satisfactory; secondary endpoints were very good partial response (VGPR), PFS2, overall survival (OS) and adverse events (AEs) during induction and maintenance.

RESULTS. 171 patients (Id 41, ICd 59, ITd 60 and IBd 11) with a median age of 74 years were enrolled and started treatment. Two of the four investigational arms were prematurely closed due to low-enrollment (IBd arm, 11 patients enrolled) and high risk of inefficacy (Id, 41 patients enrolled). Median follow-up was 27 months. After the induction phase, ICd and ITd resulted in higher ≥ PR ( 75%-84% vs. 57%; p<0.05) and VGPR (46%-48% vs 24%; p<0.05) rates as compared to Id. The median PFS was 10.3 months with Id, 17.9 with ICd, 12.3 with ITd, and 13.8 with IBd, with a 2-year PFS probability of 31%, 39%, 27% and 40%, respectively. Median OS was not reached in either arm, without significant differences in the 2-year OS across arms (Id: 85%; ICd: 75%; ITd: 78%; IBd: 89%). Grade 3-4 non-hematological AEs were more frequent in the ITd arm (45%) as compared to the Id (17%), ICd (17%) and IBd (36%) arms, as well as the risk of treatment discontinuation due to AEs: ITd 17% vs Id 10%, ICd 12%, IBd 9%.

Overall, 102 patients (60%) completed the induction phase and proceeded to ixazomib maintenance (median follow-up from start of maintenance: 18 months). The best response during maintenance was PR in 26%, VGPR in 29%, and complete response (CR) in 26% of patients; 18% of patients improved the response obtained during induction by at least one IMWG category. The median PFS from start of maintenance was 15 months. The median duration of maintenance was 12 months. All grades AEs occurred in 39% of patients during maintenance, while grade 3-4 AEs occurred in 10% of patients. Grade 1-2 peripheral neuropathy (PN) was reported in 15% of patients, without grade 3-4 events. Overall, 15% required at least one dose reduction of ixazomib and 12% discontinued ixazomib maintenance due to AEs.

CONCLUSIONS. Safety and efficacy data suggest that Id combined with cyclophosphamide was the most promising induction strategy compared to the other investigated combinations. Continuous treatment with single-agent Ixazomib confirmed its efficacy and tolerability in elderly NDMM patients.