Belantamab mafodotin, lenalidomide and dexamethasone in transplant-ineligible patients with newly diagnosed multiple myeloma: Part 1 results of a phase I/II study

Preclinical and clinical data demonstrate synergy between belantamab mafodotin (belamaf) and immunomodulatory drugs with limited overlapping toxicities. We investigated the safety and efficacy of belamaf with lenalidomide 25 mg on days 1-21 every 28 days and dexamethasone 40 mg weekly (belamaf-Rd) in transplant-ineligible patients with newly diagnosed multiple myeloma. Thirty-six patients (median age, 72.5 years) were randomized to receive belamaf at three different doses (2.5, 1.9, or 1.4 mg/kg) every 8 weeks. The dosing schedule was extended to every 12 weeks to mitigate ocular toxicity. Most common grade ≥3 adverse events were fatigue (n=21, 58.3%), rash (n=6, 16.7%), diarrhea (n=8, 22.2%) and COVID-19 (n=5, 13.9%). Grade 3-4 ocular adverse events, comprising visual acuity decline from baseline and/or keratopathy, were reported in 39/216 (18.1%), 33/244 (13.5%), and 26/207 (12.6%) ophthalmological assessments in the 2.5, 1.9, and 1.4 mg/kg cohorts, respectively. Importantly, grade 3-4 keratopathy was identified in 9/216 (4.2%), 1/244 (0.4%) and 1/207(0.5%) assessments. Most patients (32/36, 88.9%) were treated with the extended, every-12-week schedule, during which 40, 33 and 16 doses were withheld due to ocular adverse events in the 2.5, 1.9, and 1.4 mg/kg cohorts, respectively. Overall, the rates of very good partial response and better and complete response and better were 83.3% and 52.8%, respectively, without significant differences among cohorts. Over a median follow-up of 20.3 months no disease progression was reported; six patients discontinued treatment due to infection-related death (4 cases of COVID-19, 2 cases of pneumonia) and one patient withdrew consent. Based on the toxicity/efficacy balance, the recommended phase II dose was 1.9 mg/kg every 8 weeks, extended to every 12 weeks because of toxicity. In conclusion, Belamaf-Rd, with the extended schedule for belamaf, showed important clinical activity and a significant improvement of ocular adverse events with minimal impact on vision-related functioning in an elderly, non-transplant eligible population.