Prior studies have revealed that the presence of increasing number of polyclonal plasma cells (pPCs) in the bone marrow (BM) are associated with better outcomes in newly diagnosed multiple myeloma (MM) patients. This effect has not been studied in patients with MM at the time of disease relapse. We determined the prognostic value of depletion of pPCs in the BM by 7-color multiparameter flow cytometry in a series of 174 relapsing MM patients. The time to next therapy (TTNT) in those with <5% pPCs was 9.4 months versus 13.9 months in those with ≥5% pPCs (P =.0091). The median overall survival (OS) in those with <5% pPCs was 21.4 months, while the median OS was not reached in those patients with ≥5% pPCs (P =.019). Of the 109 patients with standard risk cytogenetics, the median OS of those with <5% pPCs was 28.4 months, while the median OS was not reached in those with ≥5% pPCs (P =.033). As such, <5% pPCs in the BM appears to have prognostic utility in identifying a subset of relapsing MM patients, even with standard-risk cytogenetics, who have a particularly adverse outcome.
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