Clinical implications of loss of bone marrow minimal residual disease negativity in multiple myeloma.

Multiple myeloma (MM) patients frequently attain a bone marrow (BM) minimal residual disease (MRD) negativity status in response to treatment. We identified 568 patients who achieved BM MRD negativity following autologous stem cell transplantation (ASCT) and maintenance combination therapy with an immunomodulatory agent and a proteasome inhibitor. BM MRD was evaluated by next generation flow cytometry (sensitivity of 10-5 cells) at 3 to 6 months intervals. With a median follow up of 9.9 years from diagnosis (range, 0.4 - 30.9), 61% of patients maintained MRD negativity, while 39% experienced MRD conversion at a median of 6.3 years (range, 1.4 - 25). The highest risk of MRD conversion occurred within the first 5 years after treatment and was observed more often in patients with abnormal metaphase cytogenetic abnormalities (95%vs. 84%; P = 0.001). MRD conversion was associated with a high risk of relapse and preceded it by a median of 1.0 year (range, 0 - 4.9). However, 27% of MRD conversion positive patients had not yet experienced a clinical relapse with a median follow-up of 9.3 years (range, 2.2 - 21.2). Landmark analyses using time from ASCT revealed patients with MRD conversion during the first 3 years had an inferior overall and progression-free survival compared to patients with sustained MRD negativity. MRD conversion correctly predicted relapse in 70%, demonstrating the utility of serial BM MRD assessment to complement standard laboratory and imaging to make informed salvage therapy decisions.