Prognostic Implication of Early Molecular Response at 3 Months in Chronic Myeloid Leukemia Patients: A Comparison of Imatinib and Second Generation Tyrosine Kinase Inhibitors

Background: Although several studies have demonstrated that BCR-ABL1 transcript levels at 3 months were prognostically significant in patients treated with frontline imatinib (IM) and second-generation tyrosine kinase inhibitors (2G-TKIs), the decision to change treatment based on early molecular response (EMR) status remain under investigaiton. Because CML patients currently have multiple treatment options, the impact of early molecular milestones on long-term outcomes needs to be determined in each agent treated patients.

Aims: The aim of this study is to evaluate the impact of 3-month early molecular response (EMR) on long-term outcomes of CML patients treated with IM and different 2G-TKIs, as additional information to guide clinical decisions on switching to a different TKI.

Methods: 734 new CP CML patients who were treated with frontline IM (n = 366) or 2G TKIs (n = 368) were analyzed. Molecular responses were monitored using qRT-PCR assay in 3 month intervals by achieving major molecular response (MMR), and then 6 month intervals after achieving MMR. Main study objectives were to evaluate the long-term outcomes, including failure-free survival (FFS), progression-free survival (PFS), and overall survival (OS), according to 3-month EMR. FFS was measured from the date of treatment start until death, progression to AP or BP, or ELN failure on treatment, whichever came first. PFS and OS collected survivals on patients who were treated with other TKIs after frontline therapy discontinuation.

Results: A total of 734 patients were treated with imatinib (IM; n = 366), dasatinib (DAS; n = 141), nilotinib (NIL; n = 89), and radotinib (RAD; n = 138). The median age was 43 years (range, 11-87). The percentages of patients with low, intermediate, and high Sokal risk scores were 37%, 38% and 23%, respectively, with 2% unknown risk. With a median follow-up of 85.6 (IM; range, 4.4-207.5) and 38.9 (2G-TKIs; range, 11.6-130.2) months, 460 (62.7%; 182 IM and 218 2G-TKIs) patients continue on the frontline therapy and 274 (37.3%) patients were permanently discontinued or changed to other TKIs due to intolerance (73 IM, 38 DAS, 2 NIL, 28 RAD), ELN failure (32 IM, 3 DAS, 2 NIL, 3 RAD), progression (3 IM, 1 DAS, 1 RAD), and others (60 warning, 3 pregnancy, 14 treatment-free remission study, and 9 follow-up loss). In 366 patients treated with IM, patients achieving BCR-ABL1 ≤ 10% at 3 months (n = 275, 75.1%) had a better outcomes in terms of 8-y OS (97.4% vs 89.7%, P <0.001), 8-y PFS (96.3% vs 88.6, P=0.002), and 8-y FFS (91.5% vs 74.6%, P<0.001) compared with those of the patients with BCR-ABL1 >10%. In 368 patients treated with 2G-TKIs, achievement of 3-month EMR (n = 331, 90.0%) was associated with a higher 8-y OS (98.6% vs 91.9%, P <0.001), 8-y PFS (98.2% vs 91.7, P=0.001), and 8-y FFS (96.5% vs 82.7%, P<0.001). The prognostic impact of 3-month EMR was observed in both IM and 2G-TKIs treated groups.

Conclusions: Our data showed that EMR failure at 3 months could translate into poor survival outcomes in patients treated with frontline IM and 2G-TKIs.However, to confirm the benefit of an early switch of therapy, further investigations in a larger patient population with longer follow-up are needed.