A Phase II Trial of the Combination of Ixazomib, Lenalidomide, and Dexamethasone in High-Risk Smoldering Multiple Myeloma

Background: Early therapeutic intervention in high-risk SMM (HR-SMM) has demonstrated benefit based on previous studies that included treatment with lenalidomide or lenalidomide and dexamethasone (Mateos et al. N Engl J Med 2013; Lonial et al. J Clin Oncol 2020). Combination therapy with triplets has shown higher rates of deep response and improved outcomes in patients with multiple myeloma, including the combination of ixazomib, lenalidomide, and dexamethasone (Moreau et al. N Eng J Med 2016). We present our results of phase II study of ixazomib, lenalidomide and dexamethasone in HR-SMM.

Methods: Patients enrolled on the study met eligibility for high-risk SMM based on the defined criteria proposed by Rajkumar et al. (Blood 2014). The treatment plan was designed to be administered on an outpatient basis where patients receive 9 cycles of induction therapy of ixazomib (4mg) at days 1, 8, and 15, in combination with lenalidomide (25mg) at days 1-21 and dexamethasone at days 1, 8, 15, and 22. The induction phase was followed by ixazomib (4mg) and lenalidomide (15mg) maintenance for another 15 cycles. A treatment cycle was defined as 28 consecutive days for a total of 24 months period. Bone marrow samples of all patients were obtained before starting therapy for baseline assessment for minimal residual disease (MRD) testing, whole-exome sequencing (WES), and RNA sequencing of plasma and bone marrow microenvironment cells. Moreover, blood samples were obtained at screening and before each cycle for isolating cell-free DNA (cfDNA) and circulating tumor cells (CTCs).

Results: Sixty-one patients have been enrolled in this study from February 2017 to 2020. The median age of the patients at enrollment was 64 years (range, 40 to 84), with 33 males (54.1%). The analysis was conducted on patients who have completed at least 2 cycles of therapy (n=55). Thus far, 42 (69%) patients have completed the planned 24 cycles of therapy. High-risk cytogenetics (defined as the presence of t(4;14), 17p deletion, and 1q gain) were found in 14 patients out of the 33 evaluable (42.4%) Interphase fluorescence in situ hybridization (iFISH) results. The median number of cycles completed was 24 cycles (range: 2-24). According to the new IMWG risk stratification model (20-2-20), baseline markers showed that 32 patients (58%) were high risk, 18 (33%) were intermediate risk, and 5 (9%) were low risk.

The most common grades 3 or greater toxicities were neutropenia (20%), hypophosphatemia (13%), leukopenia (11%), rash (9%), lymphocytopenia (5%), and thrombocytopenia (5%). Stem cells were collected from all eligible patients by the end of the induction phase. No patients discontinued treatment due to toxicity. At the time of data cut off, the overall response rate (partial response or better) in participants who completed at least 2 cycles of treatment was 90.9% (50 of 55), with 12 complete responses (CR, 21.8%), 10 very good partial responses (VGPR, 18.2%), 28 partial responses (50.9%), and 4 minimal responses (MR, 7.3%). ORR in patients who completed the induction phase (≥9 cycles) was 92.3% (n= 48 of 52), with 22 (40%) deep remissions including 12 (23.1%) and 10 (19.2%) having achieved a CR and VGPR, respectively. All patients who had a CR have also achieved a stringent CR. No patients developed progression to overt or active MM while on study therapy. After completion of study therapy, 4 patients progressed to active MM during follow up, 3 additional patients developed biochemical progression and started a new course of therapy but did not meet CRAB criteria and 7 patients confirmed biochemical PD and remain off therapy.

Conclusions: The combination of ixazomib, lenalidomide, and dexamethasone is an effective all oral well-tolerated intervention in high-risk smoldering myeloma that demonstrated an ORR of >90% and deep remission in >40% of patients. While no patients progressed to overt MM while on therapy, some developed progression after completion of planned study therapy, indicating the possible need for higher intensification of therapy or maintenance therapy beyond 2 years in this high-risk group of patients. Longer follow-up for disease outcome is ongoing.