Predictive Value of 3-Month Early Molecular Response in New Chronic Phase Chronic Myeloid Leukemia Patients Treated with Radotinib

Background: Recent studies have demonstrated that early molecular milestones were able to identify high-risk chronic myeloid leukemia patients treated with frontline imatinib (IM) and second generation tyrosine kinase inhibitors (2G TKIs) such as nilotinib and dasatinib. However, whether a single measurement of BCR-ABL1 transcripts level after 3 months of treatment is sufficient to define failure necessitating a change of treatment is not confirmed. Radotinib (RAD) is a 2G TKI for BCR-ABL1 tyrosine kinase, which was approved by the Korea FDA for the second-line therapy, and the phase 3 study comparing the efficacy and safety of RAD 300 and 400 mg twice daily and IM 400 mg once daily in patients with newly diagnosed CP CML was performed. The aim of this study was to identify the predictive value of 3-month molecular milestone for an achievement of major molecular response (MMR) by 12 months to RAD therapy. Additionally, in the same population, predictive factors for achieving MMR by 12 months were analyzed.

Methods: Among 241 patients who were enrolled in the randomized, open-label, phase 3 study of RAD, 236 patients with available 3-month qRT-PCR on study therapy [RAD 300 mg twice (n = 79), RAD 400 mg twice (n = 79), IM 400 mg once (n = 78)] were evaluated. Molecular responses were monitored using a qRT-PCR assay in 3-month intervals by 12 months. All qRT-PCR were tested with at least 4.5-log sensitivity in the central laboratory (Cancer Research Institute, The Catholic University of Korea, Seoul, Korea) and MMR was defined as a BCR-ABL1 transcript level of 0.1% or lower on the international scale (IS).

Results: 236 patients (including 149 men and 87 women) with available 3-month qRT-PCR on study therapy were evaluated. With a median age of 45 years (range, 18-84 years), the distribution of low, intermediate and high Sokal risk scores were 27%, 47% and 26%, respectively. At 3 months, BCR-ABL1 ≤10% [RAD 300 mg twice (n = 68), RAD 400 mg twice (n = 69), IM 400 mg once (n = 55)] and >10% [RAD 300 mg twice (n = 11), RAD 400 mg twice (n = 10), IM 400 mg once (n = 23)] were observed. In the IM 400 mg once group, patients with BCR-ABL1 ≤10% at 3 months showed a significant higher rate of MMR by 12 months compared with that of patients with BCR-ABL1 >10% (38.2% vs 13.0%, P = 0.028). In the RAD 300 and 400 mg twice group, an achievement of 3-month EMR was associated with a higher rate of MMR by 12 months [57.4% vs 18.2%, P = 0.016 (RAD 300 mg twice) and 50.7% vs 10.0%, P = 0.018 (RAD 400 mg twice)]. After adjusting for factors affecting achievement of MMR by 12 months on univariate analyses, multivariate analyses showed that b2a2 transcript type (RR of 0.46, P = 0.023), large spleen size (RR of 0.91, P = 0.001), and no achievement of 3-month EMR (RR of 0.24, P = 0.004) were predictor for not achieving MMR by 12 months. Significance of 3-month EMR for achieving MMR by 12 months was observed in the separated treatment groups: RR of 0.24, P = 0.037 in the IM 400 mg once group, RR of 0.17 P = 0.028 in the RAD 300 mg twice group, and RR of 0.11, P = 0.040 in the RAD 400 mg twice group.

Conclusions: Our results suggest that 3-month EMR can play key roles for 12-month MMR achievement in CP CML patients treated with IM and RAD. In addition, some factors for achieving 12-month MMR were detected. To evaluate the long-term prognostic value of 3-month EMR, further clinical investigations in a larger patient population with longer follow-up are needed.