The persistence of immunophenotypically normal residual bone marrow plasma cells at diagnosis identifies a good prognostic subgroup of symptomatic multiple myeloma patients.

Multiparameter flow cytometry immunophenotyping allows discrimination between normal (N-) and myelomatous (MM-) plasma cells (PCs) within the bone marrow plasma cell compartment (BMPCs). Here we report on the prognostic relevance of detecting more than 5% residual normal plasma cells from all bone marrow plasma cells (N-PCs/BMPCs) by multiparameter flow cytometry in a series of 594 newly diagnosed symptomatic MM patients, uniformly treated according to the Grupo Español de MM 2000 (GEM2000) protocol. Our results show that symptomatic MM patients with more than 5% N-PCs/BMPCs (n = 80 of 594; 14%) have a favorable baseline clinical prospect, together with a significantly lower frequency of high-risk cytogenetic abnormalities and higher response rates. Moreover, this group of patients had a significantly longer progression-free survival (median, 54 vs 42 months, P = .001) and overall survival (median, not reached vs 89 months, P = .04) than patients with less than or equal to 5% N-PCs/BMPCs. Our findings support the clinical value of detecting residual normal PCs in MM patients at diagnosis because this reveals a good prognostic category that could benefit from specific therapeutic approaches. This trial was registered at www.clinicaltrials.gov as NCT00560053.