Phase III Randomized Study of Imatinib Therapy in Chronic Phase Chronic Myeloid Leukemia Comparing Standard Dose-Escalation with Progressive Dose-Escalation (JALSG CML207 study)

Imatinib mesylate (IM) given orally at a daily dose of 400 mg was the standard of care as initial therapy for patients with chronic myeloid leukemia (CML) in the chronic phase (CML-CP), before 2^ndTKI era. Treatment guidelines by European Leukemia Net (ENL) propose dose escalation based on clinical assessments of disease response in 2006. Preclinical data and results of single-arm studies raised the suggestion that better results could be achieved with a higher dose. However, randomized study to compare high-dose IM (800 mg) with the standard dose (400 mg) as front-line in all CML high-risk patients did not support the extensive use of high-dose IM. To improve the results of CML therapy, another alternative strategy is a dose-escalation based on more aggressive clinical assessments of disease response in comparison with the standard ELN proposed.

In 2007, we conducted a prospective randomized study to compare different dose escalation programs; the standard-dose escalation program proposed by ENL (Group A) and the aggressive dose escalation program (Group B) among newly diagnosed patients with CML-CP. The aggressive dose escalation program consisted of the following interventions. If the patients do not obtained a complete cytogenetic response at 3 months or do not reach a major molecular response (MR3, IS=0.1%), IM is increased from standard dose of 400mg daily to 600 mg daily. The primary endpoint is the rate of major molecular response at 12 months, which is a surrogate for long-term progression-free survival (PFS). It is also a surrogate for complete molecular response, which is pointed out recently to be the condition for treatment free survival.

Total 248 patients entered to this study between June 16 2007 and June 15, 2011. Median age was 49 years old (range 15-69); 86 were female and 162 were male. Sokal score index was high-risk in 46 patients, intermediate-risk in 77 and low-risk in the remaining. White blood cell count at diagnosis was 43X10^9/L in median (10-881 in range). There was no significant difference between Group A (N=126) and Group B (N=127) according to these factors. Overall survival was 100%, 98% and 98% at 1, 2 and 3 years after treatment, respectively. Three patients developed blast crisis during 3 years (day 177, 272, 481) and all received hematopoietic stem cell transplantation (HSCT). Two other patients who had no cytogenetic response also received HSCT. Eleven patients (4.5%, Group A, N=8, Group B, N=3) failed to achieve complete hematological remission. The overall complete cytogenetic response (CCR) rate at 6 months after the treatment was better in Group B (89%) than in Group A (79%) with borderline significance (p=0.05, Fisher's exact test). However, the overall CCR rate at 12 months was 92% in both groups. At 12 months, MR3 was achieved in 61% and 64% of patients in Group A and Group B, respectively (p=0.69). Also, at 24 months, MR3 was achieved in 91% and 87% of patients in Group A and Group B, respectively. At 3 months, plans called for 8 and 45 patients to increase the dose of IM to 600 mg in Group A and B, respectively; however, only 4 and 27 patients followed the protocol. At 6 months, 10 and 55 patients were to increase the dose of IM to 600 mg in Group A and B, respectively; however, only 2 and 24 patients followed this protocol. The main reason was intolerance of IM. Among the patients who were to increase the dose at 3 and 6 months, 53% of those who could do according to the protocol achieved MR3 at 12 months, while only 16% of patients failed to increase (p=0.08). Eighty patients experienced drug discontinuation during 1 year. The incidence of discontinuation was 37% in Group B, whereas it was 29% in Group B (p=0.18). A substantial part of patients withdrew from this study; however, there was no difference between Groups (A 20%, B 21%).

This is the first randomized study to compare two different dose escalation programs. The aggressive dose escalation program showed a better early cytogenetic response than the standard-dose escalation program, but, failed to evidence a better molecular response in a later period. Higher efficacy of high dose IM might be cancelled by the more frequently discontinuation of IM in this group. This study concluded that aggressive dose escalation is not recommended and careful management of drug dose according to patients' condition (residual leukemia, adverse effect, emotion) might be the best way for better outcome, which is applicable to new generation TKIs.