Mobilization of CD34⁺ cells in elderly patients (≥ 70 years) with multiple myeloma: Influence of age, prior therapy, platelet count and mobilization regimen

The mobilization of peripheral blood stem cells was studied in 984 multiple myeloma patients, including 106 patients aged ≥ 70 years. Increasing age correlated inversely with CD34⁺ yield (P < 0.0001), but also with ≥ 12 months of prior standard chemotherapy (P = 0.0001), > 200 × 10⁹/I platelets (P = 0.0006) premobilization and mobilization with growth factors only (P = 0.0001). After controlling for these age covariates, multivariate analysis identified ≥ 12 months standard therapy and platelet count ≤ 200 × 10⁹/I premobilization as favourable variables (both P > 0.0001), while increasing patient age remained an unfavourable factor (P = 0.0009). With both favourable variables, 85% of elderly patients collected ≤ 4 × 10⁶/kg CD34⁺ cells in a median of one collection. The effect of age was incremental with no age threshold showing acceleration in the decline of CD34⁺ yield. Chemotherapy significantly increased CD34⁺ yield compared with growth factors only. However, the subgroup of patients with < 12 months prior therapy and premobilization platelet count > 200 × 10⁹/I mobilized as many CD34⁺ cells with granulocyte colony-stimulating factor (G-CSF) alone as with chemotherapy and haematopoietic growth factors. Increasing patient age had no effect on post-transplant neutrophil recovery, but significantly delayed platelet recovery (≤ 50 × 10⁹/I) if > 2 × 10⁶/kg CD34⁺ cells were infused, but this effect was eliminated completely with infusion of ≤ 4 × 10⁶/kg CD34⁺ cells. Increasing age adversely affected CD34⁺ yield even with limited premobilization therapy, indicating that early collection is important in elderly patients.