Previous retrospective studies have shown that serum B-cell maturation (sBCMA) levels predict outcomes among patients with multiple myeloma (MM) undergoing new treatments. Specifically, baseline levels and changes during treatment of this protein predict both progression free survival (PFS) and overall survival. However, prospective studies are lacking evaluating sBCMA for determining outcomes among MM patients undergoing new treatments. Thus, we evaluated whether its baseline levels and changes during treatment in the amount of this serum marker predict outcomes among 38 relapsed/refractory MM patients treated with ruxolitinib, lenalidomide and methylprednisolone in a phase 1 trial. Patients with baseline sBCMA levels in the lowest three quartiles had longer PFS (median PFS 136 vs. 28 days; p < 0.0001). This was also shown for patients with baseline levels above the median (median PFS 77 vs. 140 days; p = 0.0225). PFS was shorter for patients whose sBCMA levels increased >25% through their first cycle (median PFS: 50 vs 134 days, p = 0.0022), second cycle (median PFS: 50 vs 141 days, p = 0.0273), and during the first three cycles of study treatment (median PFS: 50 vs 220 days, p < 0.0001). No patient whose sBCMA increased ≥25% during cycle 1 responded whereas the majority (58%) of patients whose level increased < 25% responded. This is the first prospective study to determine whether sBCMA levels predict outcomes for MM patients undergoing a non-BCMA directed treatment regimen and demonstrates that baseline levels and its changes during treatment predict PFS and the likelihood of responding to their treatment. These results add to the growing literature suggesting that this serum marker will be useful for determining outcomes for patients undergoing treatment for MM.

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