Safety and clinical activity of belantamab mafodotin with pembrolizumab in patients with relapsed/refractory multiple myeloma (RRMM): DREAMM-4 Study.

8018 Background: Belantamab mafodotin (belamaf; BLENREP), a B-cell maturation antigen (BCMA) targeted antibody–drug conjugate approved for adult patients with RRMM, has a multimodal mechanism that eliminates myeloma cells via direct cytotoxicity and a systemic anti-tumor immune response, which may be augmented by an immune checkpoint inhibitor. DREAMM-4 (NCT03848845) assessed safety and clinical activity of belamaf with pembrolizumab (pembro) in RRMM. Methods: This was a Phase I/II, single-arm, open-label study of adults with RRMM after ≥3 lines of therapy (LOT, including anti-CD38 monoclonal antibody, proteasome inhibitor, and immunomodulator). Part 1 established the dose of belamaf 2.5 mg/kg with pembro 200 mg, both IV Q3W up to 35 cycles, for the Part 2 expansion. Primary efficacy endpoint was investigator-assessed overall response rate (ORR, ≥partial response [PR] per IMWG criteria by investigator). Secondary endpoints included duration of response (DoR), progression-free survival (PFS), adverse events (AEs) per NCI-CTCAE v4.03, and pharmacokinetics (PK). Results: This primary analysis of all treated pts (as of Oct 18, 2021) included 34 pts (6 in Part 1 and 28 in Part 2). In both parts, median prior LOT was 5 (range 3–13); 10 pts (29%) had high-risk cytogenetics and 9 (26%) had extramedullary disease. ORR was 47%, with most responses (10/16 pts) ≥ very good PR (VGPR, Table). Median follow-up was 14.7 months (mo); median (95% CI) DoR was 8.0 (2.1–not reached) mo; median PFS was 3.4 (1.4–5.6) mo. Most pts had ≥1 AE (any grade [Gr]: 97%; Gr ≥3: 74%) and treatment-related AE (TRAE, any Gr: 97%; Gr ≥3: 65%). Most common (≥35%) AEs were keratopathy (any Gr: 76%; Gr ≥3: 38%), vision blurred (any Gr: 38%; Gr ≥3: 0%), and thrombocytopenia (any Gr: 35%; Gr ≥3: 29%). AEs led to dose delays (65%) and dose reductions (32%), but not discontinuation. Nine pts had a serious AE (SAE); 4 pts had ≥1 SAE related to study treatment. Two pts had immune-related AEs of Gr 1 (gout and autoimmune hypothyroidism). Preliminary PK and soluble BCMA data were consistent with single-agent belamaf therapy. Conclusions: Belamaf + pembro demonstrated a favorable ORR compared with single-agent belamaf in heavily pre-treated RRMM. No new TRAEs were identified; AE frequency and severity were similar to single-agent belamaf. Correlative biomarker studies are ongoing. Clinical trial information: NCT03848845. [Table: see text]