Influence of Clonal Plasma Cell Contamination of Peripheral Blood Stem Cell Autografts on Progression and Survival in Multiple Myeloma Patients After Autologous Peripheral Blood Stem Cell Transplantation in Long-term Observation.

BACKGROUND: High-dose chemotherapy followed by autologous peripheral blood stem cell transplantation (auto-PBSCT) remains the mainstay of treatment of eligible patients diagnosed multiple myeloma. The role of clonal plasma cell (CPC) contamination was found as a reason for relapse, but results in terms of survival, progression, and purging were ambiguous. Therefore, the aim of the study was to explore the influence of CPC contamination in the autograft on survival and progression after auto-PBSCT.

STUDY DESIGN: The study included 59 patients diagnosed and treated for multiple myeloma in 1998-2004. Cells with coexpression of CD38+++ CD138++ CD56+ and lacking the expression of CD45, CD19, CD10, CD20, and CD23 were considered CPC in flow cytometry.

RESULTS: The risk of death and progression after auto-PBSCT increased significantly by 10% (P < .021) and 8% (P < .034) per 1 × 106 /kg of the CPC number, respectively. For CPC number above 2.96 × 106 /kg overall survival achieved clinical significance. Two years after auto-PBSCT, the risk of death was independent of CPC number among the patients who survived (P = .70). Analogous conclusions concerned results of progression-free survival at 1 year after auto-PBSCT.

CONCLUSIONS: High clonal plasma cell contamination (>2.96 ×1 06 /kg; 90th percentile of CPC number) is associated with the worst progression-free survival and overall survival. Therefore purging in vitro might be considered for the patients with the highest CPC contamination. Negative consequences of CPC contamination on the risk of death are observed for only 2 years after auto-PBSCT. Thereafter only those patients who had lower CPC contamination survived.