LINKER-MM1 study: Linvoseltamab (REGN5458) in patients with relapsed/refractory multiple myeloma.

Background: Linvoseltamab is a BCMA×CD3 bispecific antibody with encouraging efficacy and a manageable safety profile in patients (pts) with relapsed/refractory multiple myeloma (RRMM) (Bumma et al. ASH 2022). Aims: Two Phase (Ph) 2 full dose cohorts (50 mg and 200 mg) in the LINKER-MM1 (NCT03761108) trial were studied to optimize dose selection. Methods: Ph 2 enrolled adults with MM who progressed on/after ≥3 lines of therapy (LoT) including a proteasome inhibitor (PI), an immunomodulatory drug (IMiD), and an anti-CD38 antibody (Ab), or were at least triple class (IMiD/PI/anti-CD38 Ab) refractory. A protocol amendment permitted pts who progressed during 4–12 weeks on 50 mg to dose escalate to 200 mg. Primary endpoint was objective response rate (ORR). Key secondary endpoints included duration of response (DoR) and minimal residual disease status. Results: As of 1 Sept 2022, 252 pts have enrolled (Ph 1: 73; Ph 2: 179 [200 mg: 75; 50 mg: 104]). Median age was 66 years (range 37–90), 12% had extramedullary plasmacytomas, 12% high-risk cytogenetics, 37% bone marrow plasma cell percentage (BMPC) ≥50%. Median soluble BCMA concentration (sBCMA) was 0.43 mg/L (range, 0–10.2), median prior LoT: 5 (range 1–16), and 81% were ≥triple class refractory. Numerically higher efficacy was observed with 200mg, including in high disease burden subgroups; ORR was 64% (200 mg cohort; n=58, includes 12 Ph 1 pts) and 50% (50 mg cohort; n=104). Subgroup analyses showed higher ORR in the 200 mg cohort versus 50 mg for sBCMA ≥0.4 mg/L, (52% vs 37%) BMPC >67% (64% vs 35%) and revised ISS stage III (71% vs 27%). Median DoR was not reached for both cohorts (median follow-up: 2.3 months [200 mg], 4.7 months [50 mg]). Probability of maintaining response at 6 months was 89% (200 mg) and 85% (50 mg). Out of 8 pts who progressed on 50 mg and dose escalated to 200 mg, 6 (75%) achieved a response. Treatment-emergent adverse events (TEAEs) occurred in 95% (Grade [Gr] ≥3: 66%) of pts in the 200 mg cohort (n=87, includes 12 Ph 1 pts) and 100% (Gr ≥3: 80%) in the 50 mg cohort. The most common TEAEs were cytokine release syndrome (200 mg: 37% [Gr 3: 1%]; 50 mg: 53% [Gr 3: 2%]), fatigue (200 mg: 32% [Gr ≥3: 0]; 50 mg: 33% [Gr ≥3: 0]) and anemia (200 mg: 28% [Gr ≥3: 24%]; 50 mg: 40% [Gr ≥3: 36%]). Grade ≥3 ICANS occurred in 2 pts (2%) in the 200 mg cohort and 1 pt (1%) in the 50 mg cohort. TEAEs leading to treatment discontinuation occurred in 7% (200 mg cohort) and 8% (50 mg cohort) of pts. Infections occurred in 43% (Gr ≥3: 26%) in the 200 mg cohort and 59% (Gr ≥3: 31%) in the 50 mg cohort. Summary/Conclusion: Linvoseltamab 200 mg showed better efficacy compared with 50 mg, including in pts with high disease burden. The 200 mg dose had consistent efficacy across high-risk subgroups and induced responses in pts who progressed on 50 mg. Safety was consistent across Ph 2 doses. The recommended linvoseltamab dose for further development is 200 mg. Updated data with longer follow-up and complete enrollment of the 200 mg cohort will be presented at the meeting. Keywords: Plasma cells, Clinical trial, Bispecific, Multiple myeloma