BACKGROUND: We confirmed the benefit of addition of ixazomib to lenalidomide and dexamethasone in patients with relapsed and refractory multiple myeloma (RRMM) in unselected real-world population. We report the final analysis for overall survival (OS), second progression free survival (PFS-2), and the subanalysis of the outcomes in lenalidomide (LEN) pretreated and LEN refractory patients. METHODS: We assessed 344 patients with RRMM, treated with IRD (N = 127) or RD (N = 217). The data were acquired from the Czech Registry of Monoclonal Gammopathies (RMG). With prolonged follow-up (median 28.5 months), we determined the new primary endpoints OS, PFS and PFS-2. Secondary endpoints included the next therapeutic approach and the survival measures in LEN pretreated and LEN refractory patients. RESULTS: The final overall response rate (ORR) was 73.0% in the IRD cohort and 66.8% in the RD cohort. The difference in patients reaching ≥VGPR remained significant (38.1% vs. 26.3%, p = 0.028). Median PFS maintained significant improvement in the IRD cohort (17.5 vs. 12.5 months, p = 0.013) with better outcomes in patients with 1-3 prior relapses (22.3 vs. 12.7 months p = 0.003). In the whole cohort, median OS was for IRD vs. RD patients 40.9 vs. 27.1 months (p = 0.001), with further improvement within relapse 1-3 (51.7 vs. 27.8 months, p ˂ 0.001). The median PFS of LEN pretreated (N = 22) vs. LEN naive (N = 105) patients treated by IRD was 8.7 vs. 23.1 months (p = 0.001), and median OS was 13.2 vs. 51.7 months (p = 0.030). Most patients in both arms progressed and received further myeloma-specific therapy (63.0% in the IRD group and 53.9% in the RD group). Majority of patients received pomalidomide-based therapy or bortezomib based therapy. Significantly more patients with previous IRD vs. RD received subsequent monoclonal antibodies (daratumumab-16.3% vs. 4.3%, p = 0.0054; isatuximab 5.0% vs. 0.0%, p = 0.026) and carfilzomib (12.5 vs. 1.7%, p = 0.004). The median PFS-2 (progression free survival from the start of IRD/RD therapy until the second disease progression or death) was significantly longer in the IRD cohort (29.8 vs. 21.6 months, p = 0.016). There were no additional safety concerns in the extended follow-up. CONCLUSIONS: The IRD regimen is well tolerated, easy to administer, and with very good therapeutic outcomes. The survival measures in unsorted real-world population are comparable to the outcomes of the clinical trial. As expected, patients with LEN reatment have poorer outcomes than those who are LEN-naive. The PFS benefit of IRD vs. RD translated into significantly better PFS-2 and OS, but the outcomes must be accounted for imbalances in pretreatment group characteristics (especially younger age and stem cell transplant pretreatment), and in subsequent therapies.

1st Medical Department Clinical Department of Haematology 1st Faculty of Medicine and General Teaching Hospital Charles University 110 00 Prague Czech Republic

4th Department of Internal Medicine Hematology Faculty Hospital Charles University in Hradec Kralove 500 03 Hradec Kralove Czech Republic

Department of Hemato Oncology Faculty of Medicine and Dentistry Palacky University Olomouc and University Hospital Olomouc 779 00 Olomouc Czech Republic

Department of Hematology and Transfusiology University Hospital Faculty of Medicine Slovak Medical University and Comenius University 831 01 Bratislava Slovakia

Department of Hematooncology University Hospital Ostrava Faculty of Medicine University of Ostrava 708 00 Ostrava Czech Republic

Department of Internal Medicine and Hematology 3rd Faculty of Medicine Charles University and Faculty Hospital Kralovske Vinohrady 100 34 Prague Czech Republic

Department of Internal Medicine Hematology and Oncology University Hospital Brno Faculty of Medicine Masaryk University 625 00 Brno Czech Republic

Hematology and Oncology Department Charles University Hospital Pilsen 323 00 Pilsen Czech Republic

Institute of Biostatistics and Analyses Ltd 602 00 Brno Czech Republic

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