Oral melphalan at diagnosis hampers adequate collection of peripheral blood progenitor cells in multiple myeloma

Background and Objectives. Since optimal collection of peripheral blood progenitor cells (PBPC) remains crucial for high-dose therapy in patients with multiple myeloma (MM) in relapse phase or refractory to chemotherapy, we evaluated several variables that may influence mobilization. Design and Methods. Eighty-nine patients who underwent a standard mobilization procedure with cyclophosphamide (3 g/m²) and growth factors entered the study. A composite collection totalling at least 2x10⁶ CD34⁺/kg was defined as a sufficient yield: 59 patients achieved an adequate collection. A reliable factor to predict adequate yields was prior therapy: an adequate collection was obtained in 92% of patients treated with conventional non-alkylating therapy (VAD-based regimens), in 56% treated with oral melphalan and in 23% who had received intravenous melphalan. Results. The three groups were similar for most clinical features. After adjustment for several potential confounders, the probability of an adequate PBPC collection remained higher in the group treated with non-alkylating agents, with an odds ratio (OR) of 6.14 (95% confidence interval, CI=1.34, 28.13) and lower in those treated with intravenous melphalan (OR=0.08; CI=0.01-0.61), when compared to the group treated with oral melphalan. Among the other prognostic factors (stage, percentage of bone marrow plasma cells, β2-microglobulin, labeling index, isotype, monoclonal component, Bence-Jones proteinuria) evaluated at diagnosis, there was no clear association with progenitor cell yield. Interpretation and Conclusions. In conclusion, patients who are potential candidates for high-dose therapy with PBPC support should not receive conventional alkylating therapy, even orally. Alternatively, progenitor cells should be collected early in the course of MM IVIM.