⁹⁰ y-Ibritumomab Tiuxetan or Purine Analogues Severely Affect Peripheral Blood Stem Cell Mobilization: An Analysis On 248 Patients.

High-dose chemotherapy followed by autologous Peripheral Blood Stem Cell (PBSC) transplantation represents an effective option in relapsing/refractory malignant lymphoma as well as in selected solid tumors. Collection of a sufficient amount of stem cells (CD34+ ≥ 2.0×10⁶/kg) by apheresis is mandatory for the procedure. However many factors could influence the mobilization of PBSC and about 30% of patients eligible for this therapeutic option fail stem cell mobilization. Peripheral CD34+ counts of 20/μL is conventionally considered the cut-off for a successful collection.

With the aim to identify those factors affecting PBSC mobilization, we retrospectively reviewed data about our experience at European Institute of Oncology from 01/2005 to 05/2009. By evaluating the number of CD34+cells after mobilization, patients were considered as good mobilizers (peripheral CD34+ ≥ 20/μL, group A), relative poor mobilizers (peripheral CD34+ counts <20 and ≥8/ μL, group B) and absolute poor mobilizers (peripheral CD34+ counts <8/μL, group C). A total of 248 patients were enrolled into a mobilizing PBSC program; apheresis was performed when the CD34+ cell count was >5/μL. Patients characteristics were: 140 male, 108 female; median age was 51 yrs; diagnosis included: 124 Non Hodgkin Lymphoma (NHL), 50 Hodgkin Lymphoma (HL), 35 Multiple Myeloma (MM), 5 Acute Leukemia (AL) and 33 solid tumors, 1 Chronic Lymphocitic Leukemia (CLL); mean number of previous chemotherapy lines was 1 (0-9). The main mobilization regimens in hematological patients were cyclophosphamide 4g/mq (n=118) and ESHAP either followed by G-CSF (n=27) or pegylated G-CSF (n=48); the majority of patients affected by solid tumors received ICE regimen plus G-CSF (n=26).

By evaluating the number of CD34+cells after mobilization, 163 (65.7%) patients resulted good mobilizers, 43 (17.3%) patients relative poor mobilizers and 42 (17%) patients absolute poor mobilizers. All patients in group A, 31 patients in group B (72%) and 8 patients in group C (19%) collected >2.0×10⁶ CD34+cells/kg. According the Two-sided Fisher's exact test, more than 3 previous chemotherapy lines before mobilization (p<0.001), pretreatment with purine analogues (p=0.007) or ⁹⁰Y-Ibritumomab Tiuxetan (p=0.002) were found to be independent factors able to affect PBSC mobilization. In a multivariate analysis, these factors were confirmed as detrimental (purine analogs p=0.019, ⁹⁰Y-Ibritumomab Tiuxetan p=0.003).

These results could help to identify those factors affecting PBSC mobilization. To reduce poor mobilizers we suggest to anticipate mobilization program and to evaluate the opportunity to reserve purine analogs or radioimmunotherapy after collection. About 20% of patients defined as absolute poor mobilizers might successfully mobilize PBSC by lowering the CD34+ cut-off before apheresis.

No relevant conflicts of interest to declare.