Imatinib Mesylate Induces High Complete Cytogenetic and Molecular Response Rates in Children and Adolescents with Philadelphia Chromosome-Positive (Ph⁺) Chronic Myelogenous Leukemia (CML) in Chronic Phase (CP)

Imatinib mesylate (IM), a BCR-ABL tyrosine kinase inhibitor, is an effective therapy for CML in adults and has shown efficacy in children with Ph⁺ leukemias. The aim of this study was to evaluate the efficacy of IM in Ph⁺ CML patients (pts) in CP aged <18 years at diagnosis, previously untreated or resistant to Interferon (IFN). In all pts, IM therapy, started at a dose of 340 mg/m²/day, was modulated according to the hematologic parameters. Cytogenetic studies were performed on bone marrow (BM) cells at baseline and, during IM therapy, every 3 months (mo). Complete cytogenetic response (CCyR) was also confirmed by FISH. BCR-ABL transcripts were measured in the peripheral blood (PB) cells every mo and in the BM cells every 3 mo by real-time quantitative PCR (RQ-PCR). Molecular response (MolR) was defined as major in the presence of a BCRABL: ABL ratio <0.05% and as complete with a ratio <0.001. Between February 2001 and October 2007, 13 Ph⁺ CML pts (9 M and 4 F; median age 12^8/12 years) in CP were recruited from 2 pediatric centers (Rome and Padua). Eight of the 13 pts (7 M and 1 F; median age 11 years) received IM at diagnosis and 5 (3 F and 1 M; median age 14^6/12 years) after IFN therapy given at a mean dose of 6.000.000 UI/day for a median of 18 mo. All but 1 pt tolerated well IM treatment. The mean dose of IM administered was 326 mg/m²/day for untreated pts and 227 mg/m²/day for those resistant to IFN. The characteristics and followup of the pts are summarized in the Table:

Twelve of the 13 pts (92%) achieved a CCyR after a median of 4 mo (range 3–9). Eleven of the latter 12 pts were evaluated for MolR: 11/11 (100%) pts achieved a MolR, 6 major (54.5%) and 5 complete (45.5%), on BM cells after a median of 36 mo (range 9–68) and 9/11 pts (82%) on PB cells, 4 major (44.4%) and 5 complete (55.6%), after a median of 12 mo (range 4–66). To date, 12 evaluable pts are alive in CCyR: 3 after a stem cell transplantation (SCT) and 9 still receiving IM for a median time of 68 mo (range 10–89). MolR persists on BM cells in 9/9 pts (100%), 4 complete (44%), and on PB cells in 7/9 pts (78%), 4 complete. Our experience indicates that IM is highly effective in children and adolescents with Ph⁺ CML in CP, capable also of inducing high and persistent CCyR and MolR rates also in pts resistant to IFN.