Imatinib mesylate (Glivec) is a selective inhibitor of bcr-abl tyrosine kinase, 
the product of the Philadelphia chromosome, which is the hallmark of chronic 
myeloid leukaemia (CML). With imatinib, complete cytogenetic response (CCR) can 
be achieved in over 70% of newly diagnosed patients with CML. However, the 
optimal long-term management of patients who achieve CCR after imatinib is 
unknown. With longer follow-up, it is anticipated that some patients are likely 
to progress and become candidates for autologous transplantation. We studied 
filgrastim (r-metHuG-CSF) mobilisation of peripheral blood stem cells (PBSC) in 
32 patients who have achieved CCR with imatinib. Our data demonstrate that (1) 
the target CD34(+) cell yields of >/=2.0 x 10(6)/kg were attained with 
filgrastim 10 microg/kg/day, in 9/18 (50%) of patients during uninterrupted 
imatinib therapy, and in 10/14 (70%) when imatinib was temporarily withheld. The 
median CD34(+) cell yield per aphaeresis was 0.70 x 10(6)/kg (range 0.14-2.18) 
and 2.90 x 10(6)/kg (range 0.15-8.71) in the two groups, respectively 
(P&<0.005). (2) The cell yields did not correlate with the duration of imatinib 
administration. (3) There was no impact of the mobilisation procedure on the 
level of leukaemia as measured by serial blood bcr-abl levels using real-time 
quantitative PCR with either protocol. (4) bcr-abl remained detectable at low 
levels in the harvests in most but not all patients. In conclusion, filgrastim 
can safely be used to mobilise PBSC in patients who have achieved CCR with 
imatinib, but CD34(+) cell yields are significantly improved when imatinib is 
temporarily withheld.