Response rate of Imatinib in patients with Chronic Myeloid Leukemia

Abstract

Background: In Thailand, imatinib (IMT) is used as the first-line therapy for all risk scores of chronic myeloid leukemia (CML). Although IMT is typically effective, it is only recommended for low-risk CML in the international recommendations for the treatment of CML. Consequently, the response rate of IMT may vary for patients with intermediate- to high-risk CML. Regarding the response rate of IMT in Thailand is limited. Objective: This retrospective study aims to determine the response rate of IMT and the response rate when stratified by risk for CML treatment in Thailand. Materials and Methods: Newly diagnosed CML patients treated with IMT as the initial therapy at Maharaj Nakorn Chiang Mai Hospital or Lampang Hospital between January 1, 2011 and April 30, 2019 were included. The primary endpoint was the response rate, determined as the complete hematologic response rate (CHR) at 3 months, the early molecular response rate (EMR) at 6 months, or the major molecular response rate (MMR) at 12 and 18 months. The secondary endpoint was event-free survival (EFS), which was defined as loss of response, progression to accelerated phase or blast phase and death due to the disease. The prognostic risk scores were calculated according to Sokal risk, The European Treatment Outcome Study (EUTOS), and The EUTOS Longterm Survival (ELTS). Results: Of 225 CML patients, the average age was 48.0±16.6 years, and the majority were male (127/225, 56.4%). CHR at 3 months was 81.4%, EMR at 6 months was 55.8%, MMR at 12 months was 58.7%, and MMR at 18 months was 69.5%. The median EFS was 123.27 months [95% CI 86.54–NE]. Only 195 patients had sufficient information for the risk score calculation. The percentage and number of patients categorized as having low, intermediate, or high prognostic risk according to Sokal risk were 36.4% (71), 25.6% (50), and 38.0% (74), respectively. Those according to the EUTOS risk score were 68.2% (133) and 31.8% (62), respectively. Those according to the ELTS risk score were 19.5% (38), 34.9% (68), and 45.6% (89), respectively. The response rate stratified by risks, which were CHR at 3 months, EMR at 6 months, MMR at 12 months, and MMR at 18 months, showed no difference between low, intermediate, and high in all risk classifications. Conclusion: The response rate of IMT as the first-line therapy in CML patients was good. Response rates in CML patients across various risk scores did not show statistic difference, however the results might be underpower to determine the survival difference by risk score. Further investigation through prospective study is necessary. Thus, the use of IMT, regardless of the risk classification, is acceptable in Thailand.