Immunophenotypic evaluation of the plasma cell compartment in multiple myeloma: a tool for comparing the efficacy of different treatment strategies and predicting outcome.

Multiparametric immunophenotyping can be a sensitive method for analyzing the plasma cell (PC) compartment in patients with multiple myeloma because it discriminates between myelomatous and normal PCs. Using this approach, we compared the efficacy of high-dose chemotherapy followed by autologous stem cell transplantation (ASCT) with that of conventional chemotherapy. We found that ASCT provided a significantly greater reduction in the level of residual tumor PCs and with better recovery of normal PCs. This profile of coexistence of normal PCs and myelomatous PCs resembled that observed in monoclonal gammopathy of undetermined significance. We also found that treatment-induced changes in the PC compartment correlated with disease outcome. Thus, patients in whom at least 30% of gated PCs had a normal phenotype after treatment had a significantly longer progression-free survival (60 +/- 6 months versus 34 +/- 12 months; P =.02).