Long-Term Safety and Efficacy Results of Belantamab Mafodotin Plus Lenalidomide and Dexamethasone in Transplant Ineligible Patients with Newly Diagnosed Multiple Myeloma: An Updated Part 1 Analysis from the Phase 1/2 Belard Trial

Introduction The preferred upfront treatment of transplant ineligible (TI) patients (pts) with newly diagnosed multiple myeloma (NDMM) consists of the combination of lenalidomide and dexamethasone (Rd) with a third antimyeloma agent of a different mechanism of action (e.g., proteasome inhibitors or anti-CD38 monoclonal antibodies). Belantamab mafodotin (belamaf; GSK2857916), an antibody-drug conjugate targeting BCMA, has shown efficacy in pretreated MM pts, while preclinical data demonstrate synergy between belamaf and lenalidomide, with no overlapping toxicities. Thus, there is a strong rationale for investigating the belamaf-Rd triplet in TI NDMM pts.

Methods BelaRd (NCT04808037) is an open-label, phase 1/2 study conducted in Greece, aiming to enroll 66 TI NDMM pts. Eligible are adult pts with ECOG PS 0–2 and adequate organ function. Part 1 evaluates the safety/tolerability of three belamaf doses (2.5/1.9/1.4 mg/kg) plus Rd in 36 pts and establishes the recommended phase 2 dose (RP2D). In this part, belamaf is initially administered q8w and, depending on toxicity, dosing may be adjusted to q12w. Ocular exams include Snellen best corrected visual acuity (BCVA) and slit lamp corneal evaluation. Ocular symptoms are classified by CTCAE v5.0, while the Ocular Surface Disease Index (OSDI) captures dry eye disease and activities of daily living (ADL).Herein, we present updated safety and efficacy results of all Part 1 pts with an extended follow-up time (cut-off date 05/06/2023).

Results Of the 36 pts [median age: 72.5 years; male: 19 (53%)] in Part 1, 29 (81%) are still on treatment, while 7 (19%) have discontinued [6 pts due to belamaf-unrelated fatal events: (COVID-19: 1/1/2; Pneumonia: 1/1/0, for cohorts 2.5/1.9/1.4 respectively); 1 pt withdrew consent]. The median belamaf administrations and number of cycles reached were 6/7/7 and 20.0/22.5/20.0, for the respective cohorts. The most common (≥10% of pts) non-ocular ≥ Gr3 treatment-emergent adverse events were fatigue (21 pts, 58%; [7 (58%)/7 (58%)/7 (58%)]), diarrhoea (8 pts, 22%; 2 (17%)/3 (25%)/3 (25%)]), rash (6 pts, 17%; [2 (17%)/2 (17%)/2 (17%)]), COVID-19 (5 pts, 14%; [2 (17%)/1 (8%)/2 (17%)]) and insomnia (4 pts, 11%; 0/4 (33%)/0]) , while no ≥Gr3 thrombocytopenias and infusion-related reactions were reported. Regarding ≥Gr3 infections other than COVID-19, pneumonia was reported for 3 (8%) pts [1/1/1 (8%)] and lower respiratory tract infection for 1 (3%) pt [0/0/1(8%)]. Regarding ocular adverse events (OAEs), among 216/244/201 BCVA assessments in cohorts 2.5/1.9/1.4, a meaningful BCVA decline (BCVA <20/50) with at least 3 lines drop in the better seeing eye, was observed in 21 (10%)/24 (10%)/17 (8%), while BCVA ≤20/200 with at least 3 lines drop in the better seeing eye was noted in only 2 (1%)/3 (1%)/8 (4%), with a median time to resolution of 1 month. Across all cohorts, the most frequently reported ≥Gr 3 ocular symptom was decreased vision (26/665, 4%), while ≥Gr3 keratopathy was noted in <2% of assessments. Regarding OSDI, from 202/234/196 responses received, the number of "all/most” of the time worst responses in the ocular symptoms category were 6 (3%)/6 (3%)/8 (4%), while the respective proportions in the ADL category were 6 (3%)/4 (2%)/3 (2%). The overall response rate was 100% across all cohorts: More specifically CR or better was achieved by 7 (58%)/6 (50%)/6 (50%), VGPR by 3 (25%)/5 (42%)/3 (25%) and PR by 2 (17%)/1 (8%)/3 (25%) pts in cohorts 2.5/1.9/1.4, with a median time to first response of 1 month. Finally, at a median follow-up of 20.3 months, no disease progression was observed, median PFS and median time to progression were not reached (Figure 1) and responses continue to deepen across all cohorts.

Conclusions Over an extended follow-up period, the belamaf-Rd triplet has proven a safe and effective combination for the upfront treatment of TI NDMM pts, with no long-term safety signals. Furthermore, the extended dosing schedule for belamaf had a minimal impact in vision-related functioning, as very low rates of meaningful BCVA decline and “most/all” OSDI responses were noted across all cohorts, with a rapid time to resolution. Meanwhile, a very promising clinical activity is observed, with rapid, deep and durable responses across all dose levels. Consequently, after validation with bigger pt numbers, this novel combination may well be a very attractive frontline option for this vulnerable and difficult-to-treat pt population.