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

Summary. 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/l 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/l 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/l 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/l) 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.