The minimum CD34 threshold depends on prior chemotherapy in autologous peripheral blood stem cell recipients

We analysed 57 patients with non-myeloid malignancies who received a non-pu rged autologous PBSCT, All had similar mobilisation and conditioning regime ns. A high prior chemotherapy score and the number of chemotherapy lines us ed (P = 0.015 and P = 0.01, respectively) were adverse predictors of CD34 c ell yields. Lower CD34 values (P = 0.002) were seen in patients treated wit h potent stem cell toxins (BCNU, melphalan, CCNU and mustine), designated t oxicity factor 4 agents (TF4), All patients infused with grafts containing CD34 cell doses between 1.0 and 2.0 x 10(6)/kg (range 1.25-1.90) engrafted by day 51. The only variable associated with slow platelet recovery was exp osure to TF4 (P = 0.007), The majority of patients with CD34 >1.0 x 106/kg achieved rapid and sustained engraftment and the only predictive factor of delayed recovery is prior exposure to stem cell toxins, Potential PBSCT can didates should if possible avoid first line and salvage chemotherapy contai ning TF4 drugs. We therefore advocate a minimum CD34 threshold of >1.0 x 10 (6)/kg in patients without extensive prior chemoradiotherapy, and greater t han or equal to 2.0 x 10(6)/kg in all other patients.