Results of Imatinib Dose Escalation After 36 Months of Follow-up in Chronic Myeloid Leukemia Patients with Failure or Sub-Optimal Response According to 2006 EuropeanLeukemia Net (ELN) Criteria.

Imatinib mesylate (IM) given at a daily dose of 400 mg currently represents the gold standard of care for patients with chronic myeloid leukemia (CML) in chronic phase (CP). European LeukemiaNet (ELN) guidelines propose IM dose escalation to rescue those CML patients with either suboptimal response or drug resistance. We report on the long-term efficacy of IM dose escalation in 74 patients with CP-CML after suboptimal response or failure to IM conventional dose.

Median age was 50 years (range 19-85), there were 52 males and 22 females. Thirteen patients were classified as hematologic failure (10 primary and 3 secondary), 57 patients as cytogenetic resistance (24 primary and 33 acquired). Three patients escalated the dose for cytogenetic suboptimal response and one patient for molecular suboptimal response at 18 months. Fifty-four received IM dose escalation from 400 to 600 mg and 20 patients from 400 to 800 mg.

Overall, after a median follow-up of 36 months, 68/74 (91.8%) patients maintained or achieved a complete haematologic response (CHR); this was maintained in all patients who escalated the dose for cytogenetic failure or suboptimal response. A major cytogenetic response (MCyR) was achieved in 41 patients (72%) who escalated the dose for cytogenetic failure and in 6/13 (46%) patients who escalated imatinib for hematologic failure (p=0.002). Overall, complete cytogenetic responses (CCR) were achieved in 27 (37%) out of 74 CML patients: of the 13 hematologic failure patients, only 5 achieved CCyR: all patients had prior acquired resistance to imatinib. Of the 57 cytogenetic failure, 22 reached CCR: this response was obtained in 27% of the primary cytogenetic resistant, and in 50% of the acquired cytogenetic resistant patients (p=0.02).

Three patients who escalated the dose for cytogenetic suboptimal response obtained CCR and complete molecular response (CMR), whereas one patient who escalated the dose for molecular suboptimal response at 18 months did not obtain CMR. Median time to cytogenetic response was 3.5 months. Cytogenetic responses occurred in 37/50 patients who escalated the dose to 600 mg and in 10/20 patients who escalated to 800 mg daily (p=0.234). CMR was obtained in 10 patients: in 7 patients who escalated the dose for cytogenetic failure and in 3 patients who escalated imatinib for suboptimal cytogenetic response. Estimated 2 year-progression free survival (PFS) and overall survival (OS) is 87% and 85% respectively. Sixteen patients (21.6%) experienced toxicities and had temporarily IM interruption.

Imatinib dose escalation can induce sustained responses in a subset of patients with cytogenetic resistance and a prior suboptimal cytogenetic response to standard-dose imatinib, whereas it appears less effective in haematologic failure patients or in molecular sub-optimal responders. The availability of second generation TKI should be taken into account in these letter categories of patients.

No relevant conflicts of interest to declare.