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, b2-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.