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)
Authors: Giona Fiorina , Putti Maria Caterina , Moleti Maria Luisa , Nanni Mauro , Testi Anna Maria , Varotto Stefania , Gottardi Enrico Marco , De Vellis Annalisa , Nunes Vittorio , Diverio Daniela , Leszl Anna , Saglio Giuseppe , Foà Robert 
Published: April 2020

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 &lt;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 &lt;0.05% and as complete with a ratio &lt;0.001. Between February 2001 and October 2007, 13 Ph+ CML pts (9 M and 4 F; median age 128/12 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 146/12 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:

Sex/Age at diagn/Age at treat (yrs) IFN duration/%Ph+ IM mg/m2/day CCyR/time (mo) Max Bcr-Abl:Abl (%)/time (mo) (BM) Max Bcr-Abl:Abl (%)/time (mo) (PB) CCyR duration (mo) Follow-up .F/11/146/12 40 mo/100 193.5 4 0/60 0/4 +80 Alive CCyR, Bcr-Abl:Abl (%)BM 0 PB 0.0023 F/179/12/1810/12 9 mo/100 182 6 1.27/9 0.89/9 +7 Lost to follow-up in CCyR at + 13 mo M/91/12/117/12 26 mo/50 208 3 0/36 0/12 +65 Alive CCyR, Bcr-Abl:Abl (%)BM 0 PB 0 F/89/12/910/12 13 mo/50 350 3 0/44 0/66 +66 Alive CCyR, Bcr-Abl:Abl (%)BM 0.009 PB 0 M/172/12/189/12 18 mo/80 205 9 0.029/68 0.114/72 +82 Alive CCyR, Bcr-Abl:Abl (%)BM 0.05 PB 0.15 M/126/12 −/100 310 4 0/42 0/30 +66 Alive CCyR, Bcr-Abl:Abl (%): BM 0 PB 0 M/161/12 −/100 327 n.e. n.e. n.e. n.e. IM tox; alive CCyR after SCT (sibl) (+40 mo) M/144/12 −/100 291 4 0/42 0/24 +61 Alive CCyR, Bcr-Abl:Abl (%) BM 0 PB 0 M/811/12 −/100 357.5 6 0.044/9 0.057/9 CyRel/33 Alive CCyR after SCT (+ 8 mo) M/95/12 −/100 326 3 0.013/12 0.028/9 +12 Alive CCyR,Bcr-Abl:Abl (%) BM 0.013 PB 0.15 M/410/12 −/100 328.5 3 0.02/9 0/12 BMT/+13 SCT (sibl) in CCyR-&gt;Alive in CCyR +43 mo M/137/12 −/100 349 6 0.012/30 0.025/30 +32 Alive CCyR, Bcr-Abl:Abl (%) BM 0.012 PB 0.025 F/94/12 −/100 320 3 0.009/9 0.003/9 +7 Alive CCyR, Bcr-Abl:Abl (%) BM 0.02 PB 0.003

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.