Minimal Clonal Plasma Cell Contamination of Peripheral Stem Cell Grafts Has an Adverse Prognostic Impact in Patients with Multiple Myeloma Undergoing Autologous Transplantation.

INTRODUCTION

The significance of autografts' contamination by clonal plasma cells on clinical outcome in newly diagnosed multiple myeloma (NDMM) remains controversial.

METHODS

We retrospectively reviewed the clinical and laboratory data of NDMM patients who underwent autologous stem cell transplantation (ASCT) and had received graft minimal residual disease (gMRD) examination by multi-color flow cytometry.

RESULTS

From January 2011 to December 2022, 250 NDMM patients with complete cytogenetic information, gMRD information, and who received ASCT as consolidation were enrolled. Multi-flow cytometry can achieve a median detection sensitivity of 0.004%, and gMRD positivity was 12.4% at a median level of 0.0160% (interquartile range, 0.0049%, 0.05394%). Its presence was correlated with response to induction treatment, with percentages of 2.65%, 12.94%, 28.89%, and 57.14% of patients achieving complete response, very good partial response, partial response, and minimal response/stable disease, respectively. gMRD (+) patients had a higher risk of not achieving bone marrow MRD negativity post-ASCT. After a median follow-up of 33.5 months for the whole cohort, patients in the gMRD (+) group had significantly worse progression-free survival (PFS) than those in the gMRD (-) group did (34.8 vs. 65.0 months, p = 0.001). Multivariable analysis revealed that gMRD (-) was independently predictive of better PFS (hazard ratio 0.464, 95% confidence interval: 0.274-0.785, p = 0.004). We found the significance of gMRD on PFS was in high-risk subgroups and in patients who achieved ≤ partial response prior to ASCT.

CONCLUSIONS

In conclusion, gMRD (+) was an independent risk factor for inferior progression-free survival, with the impact primarily affecting high-risk groups and patients who achieved ≤ partial response before ASCT.