Response rates and minimal residual disease outcomes as potential surrogates for progression-free survival in newly diagnosed multiple myeloma.

Progression-free survival (PFS) is a common primary endpoint in newly diagnosed multiple myeloma (NDMM). Patients with NDMM typically have longer PFS and are more likely to achieve minimal residual disease (MRD) or complete response (CR) compared to patients with relapsed or refractory multiple myeloma. Response-based surrogate endpoints may hold value given the longer follow-up time required to evaluate PFS in NDMM. In this work, systematic literature reviews of Medline, Embase, and Cochrane databases (2010-06/2020) and relevant congresses (2018-2020) were performed to identify randomized clinical trials (RCTs) and real-world studies in NDMM reporting median PFS and objective response. Associations between PFS and each response endpoint were evaluated using Pearson's product-moment correlation weighted by sample size in each RCT arm. Unadjusted and adjusted weighted linear regression models were applied to estimate the gain in median PFS associated with each response endpoint. Statistically significant correlations were identified for median PFS with overall response rate (ORR; Pearson r = 0.59), CR (r = 0.48), stringent CR (sCR; r = 0.68), and MRD (r = 0.69). The unadjusted models estimated 0.50 (95% CI: 0.36, 0.64; p<0.001), 0.42 (95% CI: 0.25, 0.58; p<0.001), 1.05 (95% CI: 0.58, 1.52; p<0.001), and 0.35 (95% CI: 0.12, 0.58; p = 0.006) months of median PFS gained per point of ORR, CR, sCR, and MRD, respectively. Associations for median PFS remained statistically significant in models adjusted for age and treatment type with ORR (0.35, 95% CI: 0.21, 0.49; p<0.001), and adjusted for age and International Staging System risk stage with CR (0.29, 95% CI: 0.16, 0.41; p<0.001). Due to small sample size, adjusted models could not be constructed for sCR or MRD. Nevertheless, evidence of significant survival benefit (p<0.05) associated with MRD negativity and sCR was identified across real-world studies. These findings provide support for the use of response outcomes as surrogate endpoints to estimate PFS benefit in NDMM.