Serial measurements of circulating plasma cells before and after induction therapy have an independent prognostic impact in patients with multiple myeloma undergoing upfront autologous transplantation.

Circulating plasma cells at diagnosis, prior to auto-transplant and at relapse have a negative impact on survival in multiple myeloma. However, the impact of kinetics of circulating plasma cells along the course of illness has not been defined. We have analyzed 247 newly diagnosed multiple myeloma patients undergoing early auto-transplant who had paired evaluation of circulating plasma cells at diagnosis and pre-transplant by 6-color flow cytometry. A total of 117 patients had no detectable circulating plasma cells at both time points (CPC-/-), 82 had circulating plasma cells at diagnosis followed by complete eradication after induction (CPC+/-) and 48 had circulating plasma cells at transplant, including persistence of cells (CPC+/+; n=45) or emergence of new cells (CPC-/+; n=3) after induction. The rate of post-transplant stringent complete response was 32% in the CPC-/-, 30% in CPC+/- and 12% in CPC+/+ or -/+ groups ( P =0.018). At a median follow up of 58 months from transplantation, the median progression-free survival in the 3 respective groups were 30, 24 and 14 months, and the 5-year overall survival rates were 83%, 70% and 43% ( P <0.001 for both comparisons). On a multivariate analysis for overall survival, the risk of mortality was higher in CPC +/- (hazard ratio 2.7, 95%CI: 1.3-5.8; P =0.009) and CPC+/+ or -/+ (hazard ratio 5.7, 95%CI: 2.5-13.1; P <0.001) groups compared to the CPC-/- group. Monitoring for circulating plasma cells before induction therapy and before transplant by 6-color flow cytometry is predictive of survival in newly diagnosed myeloma and should be incorporated into clinical trials.