Abstract
PURPOSE: High-dose chemotherapy with hematopoietic stem-cell rescue is increasingly being used in the treatment of multiple myeloma. Bone marrow and also peripheral blood stem-cell (PBSC) grafts contain measurable quantities of plasma cells, the biological significance of which is unknown. METHODS: Patients with multiple myeloma were mobilized with chemotherapy and filgrastim. The number of CD38++/CD138+ cells/kg in the grafts for autologous transplantation was determined by flow cytometry. Patients were stratified into two groups (threshold 4.5 x 10(5) plasma cells kg(-1)) of reinfused plasma cells in the first autologous graft. RESULTS: The median statistical progression-free survival was 14 months (4-34 months) in the high-contamination group (>4.5 x 10(5) plasma cells kg(-1)) compared to 26 months (4-43 months) in the low-contamination group (<4.5 x 10(5) plasma cells kg(-1), P =0.0096). Patients with 13q deletion were more frequently found to have a high contamination of the stem-cell graft with malignant plasma cells. CONCLUSIONS: Patients with graft contamination of more than 4.5 x 10(5) plasma cells kg(-1) had a high risk of early disease progression after high-dose chemotherapy. In vivo tumor cell purging prior to mobilization chemotherapy might be one strategy to improve the time to progression of high-risk patients.