DREAMM-9: PHASE I STUDY OF BELANTAMAB MAFODOTIN PLUS STANDARD OF CARE IN PATIENTS WITH TRANSPLANT-INELIGIBLE NEWLY DIAGNOSED MULTIPLE MYELOMA

ABSTRACT

Background: The bortezomib, lenalidomide, and dexamethasone (VRd) regimen is a standard of care for newly diagnosed multiple myeloma (NDMM). Belantamab mafodotin (belamaf) is a B-cell maturation antigen-binding antibody-drug conjugate that eliminates myeloma cells by a multimodal mechanism direct cell kill and anti-myeloma tumor immune response. Belamaf has demonstrated deep and durable responses as a monotherapy in the DREAMM-2 study of patients (pts) with relapsed/refractory multiple myeloma (RRMM). Preclinical evidence of belamaf in combination with bortezomib or lenalidomide suggests enhanced anti-myeloma activity, providing rationale for this treatment combination. Aims: To evaluate the safety and tolerability of this combination in adult pts with transplant-ineligible (TI) NDMM and establish the recommended Phase III dose. Methods: DREAMM-9 (NCT04091126) is an ongoing Phase I, open-label, randomized study of belamaf + VRd. The belamaf dose cohorts currently being evaluated are Cohort 1 (1.9 mg/kg Q3/4W), Cohort 2 (1.4 mg/kg Q6/8W), Cohort 3 (1.9 mg/kg Q6/8W), Cohort 4 (1.0 mg/kg Q3/4W), and Cohort 5 (1.4 mg/kg Q3/4W). Belamaf is given with VRd Q3W until Cycle 8, and with Rd Q4W thereafter. After evaluation of safety data for Cohort 1, Cohorts 2-5 were opened in parallel and enrolled pts were randomized 1111. Primary endpoint is safety. Secondary endpoints include efficacy, tolerability, and pharmacokinetics (PK). Results: As of data cutoff (07 Dec 2021), 64 pts were analyzed across all cohorts. Median age (range) was 73.0 (51- 88) years, 55% were male, 80% were white, 8% had extramedullary disease, 59% were International Staging System stage II or III, 20% had amp1q, and 17% had high-risk cytogenetics (≥1 of t(4;14), t(14;16), del17p). The median duration of follow-up varied Cohort 1 (17.4 months [mo]), Cohort 2 (5.9 mo), Cohort 3 (6.1 mo), Cohort 4 (4.7 mo), Cohort 5 (5.8 mo). Median number of belamaf cycles were Cohort 1 (6), Cohort 2 (3), Cohort 3 (3.5), Cohort 4 (4.5), and Cohort 5 (5). Most common adverse events (AEs) across cohorts included thrombocytopenia (49%), constipation (43%), diarrhea (32%), and peripheral sensory neuropathy (30%). AEs related to study treatment were experienced by 61 (97%) pts. Belamaf-related grade 3/4 AEs occurred in 24 (38%) pts. Belamaf dose reductions occurred in 11 (18%) pts, with dose delays in 10 (16%) pts. Three pts experienced a fatal severe AE (unrelated to study treatment);2 due to COVID-19 infection, 1 due to pancreatic adenocarcinoma. Early deep responses were observed;67-92% pts achieved ≥very good partial response (VGPR) (Table), with median time to VGPR of 2.1-2.9 months across cohorts. Of pts with ≥VGPR, 17 were minimal residual disease (MRD) negative, 10 in Cohort 1. As of data cutoff, 8-75% of pts achieved best response of complete response (CR) or stringent CR (sCR). Grade 3 corneal exam findings were reported in 25-58% of pts;grade 3 visual acuity changes were reported in 21-75% of pts. No grade 4 corneal exam findings or visual acuity changes were reported in pts receiving belamaf Q6/8W, compared with 0-17% and 0-8%, respectively, in the Q3/4W cohorts. Belamaf PK profile was similar to that in pts with RRMM, accounting for baseline characteristics. Image Summary/Conclusion: Belamaf + VRd demonstrated high response rates in pts with TI NDMM, with a high rate of MRD negativity indicating deep responses. No new safety signals were observed relative to DREAMM-2. Study is ongoing to evaluate the safety and efficacy of variable dose intensities of belamaf in combination with VRd.