Birtamimab in patients with Mayo stage IV AL amyloidosis: Rationale for confirmatory affirm-AL phase 3 study.

TPS8076 Background: Light chain (AL) amyloidosis is a progressive and typically fatal disorder caused by misfolded AL protein produced by plasma cells. Birtamimab is a monoclonal antibody designed to neutralize circulating soluble and deposited insoluble amyloid, thus promoting phagocytic clearance. In 2018, the phase 3 VITAL study in newly diagnosed, treatment-naive patients was terminated based on futility analysis of the primary endpoint (time to all-cause mortality [ACM] or time to cardiac hospitalization > 90 days after first study drug infusion); the final hazard ratio (HR) numerically favored birtamimab + standard of care (SOC) over placebo + SOC (0.835 [95% CI: 0.5799, 1.2011]; p = 0.330). Post-hoc analysis of ACM over 9 months revealed a substantial survival benefit (HR = 0.413 [95% CI: 0.191, 0.895]; p = 0.025) in patients at high risk for early death (Mayo Stage IV). Post-hoc analyses of secondary endpoints in this subgroup indicated meaningful improvements in health-related quality of life (assessed with 36-Item Short Form Health Survey version 2; SF-36v2) and 6-minute walk test (6MWT) distance with birtamimab + SOC (p < 0.05) at 9 months. Methods: The phase 3, double-blind, placebo-controlled AFFIRM-AL study (NCT04973137) will enroll up to 150 Mayo Stage IV patients with newly diagnosed, untreated AL amyloidosis. Patients will be randomized (2:1) to 24 mg/kg intravenous birtamimab or placebo every 28 days. Both arms will receive concomitant chemotherapy with a first-line bortezomib-containing regimen, with or without daratumumab (D), at the discretion of the investigator. Patients will be stratified at randomization based on their 6MWT distance ( < 300 vs ≥300 meters) and initiation of D. The primary efficacy endpoint is time to ACM. Secondary endpoints are change from baseline to month 9 in the physical component summary of the SF-36v2 and 6MWT distance. This trial is powered at a significance level of 0.1 under a Special Protocol Assessment (SPA) with the U.S. Food and Drug Administration (FDA). Given the > 50% relative risk reduction for ACM observed in the post-hoc analysis of VITAL for patients with Mayo Stage IV disease, the AFFIRM-AL study is designed to confirm this effect of birtamimab. Approximately 130 global sites are planned; site initiation and patient randomization are underway. Conclusion: Treatments that improve survival in AL amyloidosis are needed, particularly for patients with advanced cardiac involvement, as median overall survival for those with Mayo Stage IV disease is ̃6–9 months. The AFFIRM-AL study is designed to confirm the survival benefit observed in the VITAL study in patients with Mayo Stage IV AL amyloidosis. Clinical trial information: NCT04973137.