MRD dynamics during maintenance for improved prognostication of 1280 myeloma patients in TOURMALINE-MM3 and -MM4 trials

: Measurable residual disease (MRD) evaluation may help to guide treatment duration in multiple myeloma (MM). Paradoxically, limited longitudinal data exist on MRD during maintenance. We investigated the prognostic value of MRD dynamics in 1280 transplant-eligible and -ineligible patients from the TOURMALINE-MM3 and -MM4 randomized, placebo-controlled, phase 3 studies of 2-year ixazomib maintenance. MRD status at randomization showed independent prognostic value (median progression-free survival [PFS]: 38.6 vs 15.6 months in MRD- vs MRD+ patients, HR 0.47). However, MRD dynamics during maintenance provided more detailed risk stratification. A 14-month landmark analysis showed prolonged PFS in patients converting from MRD+ to MRD- status vs those with persistent MRD+ status (76.8% vs 27.6% 2-year PFS rates). Prolonged PFS was observed in patients with sustained MRD- status vs those converting from MRD- to MRD+ status (75.0% vs 34.2% 2-year PFS rates). Similar results were observed at a 28-month landmark analysis. Ixazomib maintenance vs placebo improved PFS in patients who were MRD+ at randomization (median 18.8 vs 11.6 months, HR 0.65) or at the 14-month landmark (median 16.8 vs 10.6 months, HR 0.65); no difference was observed in patients who were MRD-. This is the largest MM population undergoing yearly MRD evaluation during maintenance reported to date. We demonstrate the limited prognostic value of a single timepoint MRD evaluation, because MRD dynamics over time substantially impact PFS risk. These findings support MRD- status as a relevant endpoint during maintenance and confirm the increased progression risk in patients converting to MRD+ from MRD- status.