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 25mg on days 1-21 every 28 days and dexamethasone 40mg weekly (belamaf-Rd) in transplant ineligible patients with newly diagnosed multiple myeloma. 36 patients (median age 72.5 years) were randomized to receive belamaf at three different doses (2.5/1.9/1.4 mg/kg) every 8 weeks (q8w). Dosing schedule was extended to every 12 weeks (q12w) to account for ocular toxicity. Most common ≥ Grade (Gr) 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%). Gr 3-4 ocular adverse events (OAEs), comprising of visual acuity decline from baseline and/or keratopathy, were reported in 39/216(18.1%)/ 33/244(13.5%)/ 26/207(12.6%) ophthalmological assessments in cohorts 2.5/1.9/1.4 mg/kg. Importantly, Gr 3-4 keratopathy was identified in 9/216 (4.2%)/ 1/244(0.4%)/ 1/207(0.5%) assessments. Most patients (32/36, 88.9%) were treated in the extended q12w schedule, where dose holds due to OAEs were 40, 33 and 16 in cohorts 2.5/1.9/1.4. Overall, ≥VGPR and ≥CR rates were 83.3% and 52.8%, without significant differences among cohorts. Over a median follow-up of 20.3 months no disease progression was reported; 6 patients discontinued treatment due to infection-related death (n=4 COVID-19, n=2 pneumonia) and 1 patient withdrew consent. Based on toxicity/efficacy balance, the recommended phase 2 dose was 1.9 mg/kg q8w, extended to q12w for toxicity. Belamaf-Rd, with the extended schedule for belamaf, has shown important clinical activity and a significant improvement of OAEs with minimal impact on vision-related functioning in an elderly, non-transplant eligible population.