BCR-ABL1 transcript levels at 4 weeks have prognostic significance for time-specific responses and for predicting survival in chronic-phase chronic myeloid leukemia patients treated with various tyrosine kinase inhibitors.

The present study aimed to assess the clinical impact of BCR-ABL1 transcript levels determined at an earlier time point than the 3-month early molecular response (EMR) in chronic-phase chronic myeloid leukemia (CML-CP) patients. BCR-ABL1 transcript levels of CML-CP patients (n = 258; median age, 43 [range, 18-81] years) treated with various tyrosine kinase inhibitors (TKIs) were determined at 4 weeks (28 ± 3 days) and at every 3 months of treatment initiation. At 4 weeks, receiver operating characteristic curves revealed that cutoff values of BCR-ABL1 transcripts for achieving major molecular responses (MMRs) by 12 and 60 months were 40.89% and 39.16%, respectively (95% CI, 0.658-0.772 and 95% CI, 0.643-0.758; P < 0.0001). With 40% of BCR-ABL1 transcripts at 4 weeks (very early MR; VEMR), patients with VEMR achieved higher 3-month EMR and 4-week VEMR significantly associated with higher cumulative incidences of 5-year MMR (89.1% vs 72.3%; P < 0.001) and 5-year deep molecular response (DMR) (56.5% vs 29.4%; P = 0.001). Furthermore, event-free survival (EFS)-a (93.0% vs 84.8%; P = 0.068) and EFS-b (71.1% vs 57.9%; P = 0.061) by 5 years were also marginally significant. VEMR and 3-month EMR were achieved in 89 patients, with significantly superior outcomes. In multivariate analyses, lower leukocyte count (P = 0.008) and frontline second-generation TKI therapy size (P < 0.001) were significantly associated with VEMR achievement, but not baseline BCR-ABL1 level and CML duration. In conclusion, the 4-week BCR-ABL1 transcript levels including VEMR could be important to predict long-term outcomes and may provide additional information about innate intrinsic sensitivity to CML among individuals.