Rapid reduction in BCR-ABL1 transcript predicts deep molecular response in dasatinib-treated chronic-phase chronic myeloid leukaemia patients.

Objectives: We conducted a phase-II study to evaluate the efficacy and safety of dasatinib in patients newly diagnosed with chronic-phase chronic myeloid leukaemia (CML-CP) in Japan (IMIDAS PART 2 study).

Methods: Seventy-nine patients were administered 100 mg dasatinib once daily. We examined pretreatment and post-treatment influences of various factors. The BCR-ABL1 international scale (IS), halving time (HT) and reduction rate of BCR-ABL1 transcript within the initial 1 or 3 months of therapy (RR-BCR-ABL1 ) were the post-treatment factors investigated to predict the molecular response.

Results: The estimated major molecular response (MMR), molecular response 4.0 (MR4.0) and molecular response 4.5 (MR4.5) rates were 77.2%, 49.4% and 35.4%, respectively, at 12 months. Grade 3/4 non-haematologic adverse events were infrequent. Multivariate analysis showed that age >65 years was significantly correlated with MR4.0 and MR4.5 (deep molecular response: DMR) at 12 months. All post-treatment factors at 3 months predicted DMR by univariate analysis. However, RR-BCR-ABL1 was the only significant landmark for predicting DMR by multivariate analysis.

Conclusions: Primary treatment of CML-CP with dasatinib enabled early achievement of MMR and DMR, particularly in elderly patients, with high safety. Furthermore, RR-BCR-ABL1 was found to be a more useful predictor of DMR than HT-BCR-ABL1 and BCR-ABL1 IS.