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Peripheral blood stem cell (PBSC) harvesting in the smallest children (weight <10 kg) using separators is complicated by specific problems. The volume of the separation set exceeds 25% of the total blood volume and the vascular access is generally not sufficient. Therefore, a simple manual technique for PBSC harvesting was developed. Three children (6-9 kg), with newly diagnosed tumours were scheduled to be treated with three to six sequential courses of high-dose chemotherapy, each followed by PBSC support. PBSC harvests were started after mobilization using cyclophosphamide and G-CSF when the peripheral blood CD34+ cell count exceeded 50/microl. About 50 ml of blood was drawn from a venous catheter, injected into a transfer bag containing ACD-A, and centrifuged. The buffy coat obtained was pooled in a collection bag, remaining plasma and erythrocytes were immediately reinfused and a subsequent cycle started. From three to 13 cycles were performed in 1-3 days and 18.0-32.2 x 10(6) CD34+cells/kg were collected. We did not detect any bacterial contamination or any notable complications. Fifteen PBSC reinfusions have been performed to date, each with rapid engraftment taking between 7 and 13 days. Patients are in very good PR (18 months from diagnosis) or in CR (6 and 8 months). We can conclude that this procedure is feasible and safe.

Cryptic translocation t(12;21)(p13;q22) which give origin to the ETV6/RUNX1 hybrid gene can be found by I-FISH in approximately 20–25% of children with B precursor ALL as the most frequent specific aberration. This translocation is generally associated with good outcome. Despite of its favorable prognostic value, late relapses may occur within this group of patients. One of the reasons could be the high instability of the genome of leukemic cells, which is manifested at the chromosomal level by additional aberrations and/or complex chromosomal rearrangements. The aim of the study was to evaluate the significance of the additional chromosomal aberrations for prognosis of children with ETV6/RUNX1 positive ALL. For the assessment of ETV6/RUNX1 fusion gene RT-PCR and/or double target interphase FISH with locus-specific probe (Abbott-Vysis, Des Plaines, Illinois, USA) were used (200 interphase nuclei analyzed, cut-off level 2.5% tested on controls, standard deviation ≤0.5%). Karyotypes were analyzed by conventional and molecular cytogenetic methods. Structural and/or complex chromosomal aberration were verified by FISH with whole chromosome painting probes (Cambio, Cambridge, UK) and/or by mFISH with the "24XCyte" probe kit (MetaSystems GmbH, Altlussheim, Germany). We performed prospective and retrospective study of 107 children with ALL and ETV6/RUNX1 fusion gene detected by RT-PCR and/or I-FISH. Patients were diagnosed between 1995 and 2006, age ranged between 15 months and 16.9 years (median 4.2 years). Relapse appeared in 19 children (17.8%), four of them died. In 64 children (59.8%) we found besides t(12;21)(p13;q22) additional chromosomal aberrations, the most frequently trisomy or tetrasomy of chromosome 21 (20 cases), deletion of non-translocated ETV6 allele (24 cases), deletion of 6q (7 cases) and/or rearrangements of the long arm of chromosome X (6 cases). Complex karyotypes were identified in 38 children (35.5%). In twelve of them variant translocations of chromosomes 12 and 21 with other partners were observed. Event-free survival (EFS) was significantly shorter in patients with additional structural and/or complex aberrations in ETV6/RUNX1 positive cells (p=0.01). In our cohort complex karyotypes indicated poor prognosis. Finding of complex chromosomal aberrations in leukemic cells is accompanied by higher risk of relapse even in those cases where the prognostically positive aberration is primarily present.