Early measurement of CD34+cells in peripheral blood after cyclophosphamide and granulocyte colony-stimulating factor treatment predicts later CD34+mobilisation failure and is a possible criterion for guiding "on demand" use of plerixafor

Background. Early identification of predictive factors of failure to mobilise CD34+ cells could enable rational use of plerixafor during first mobilisation, avoiding the need for a second mobilisation course. However, "on demand" administration of plerixafor needs to be driven by established parameters to avoid inappropriate use. Materials and methods. To address this issue, we studied the value of the peripheral blood CD34+ count, measured early (on days +10, +11, +12 and +13), in predicting the mobilisation outcome in the ensuing days. We retrospectively collected data from three Italian centres on 233 patients affected by multiple myeloma or lymphoma who underwent a first or second attempt at mobilisation with cyclophosphamide 4 g/m(2) and granulocyte colony-stimulating factor. To assess the diagnostic value of peripheral blood white blood cell and CD34+ cell counts with respect to "mobilisation failure", we considered failed mobilisation as "disease" and the CD34+ cell count in peripheral blood, on a specific day, as a "diagnostic test". For various thresholds, we measured sensitivity, false positive rate, specificity and positive predictive value (PPV) as well as the area under the receiver-operating characteristic curves (AUC). Results. A CD34+ cell count <10x10(6)/L on day 13 had high sensitivity (1.00) and high specificity (1.00) for predicting subsequent mobilisation failure, with an AUC of 1.0. However, good prediction was also obtained using a lower threshold (CD34+ cell count: <6x10(6)/L) at an earlier time (day 12). The PPV of the day 13 threshold was 1.00 while that of the day 12 one was 0.87. Discussion. We propose that patients with <6x10(6)/L CD34+ cells in peripheral blood on day 12 and <10x10(6)/L on day 13 following mobilisation with cyclophosphamide 4 g/m(2) and granulocyte colony-stimulating factor are candidates for "on demand" use of plerixafor, making the administration of this expensive agent more efficient and avoiding its inappropriate use.