Abstract 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 ‐ ABL 1 international scale ( IS ), halving time ( HT ) and reduction rate of BCR ‐ ABL 1 transcript within the initial 1 or 3 months of therapy ( RR ‐ BCR ‐ ABL 1 1m,3m ) were the post‐treatment factors investigated to predict the molecular response. Results The estimated major molecular response ( MMR ), molecular response 4.0 ( MR 4.0) and molecular response 4.5 ( MR 4.5) 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 MR 4.0 and MR 4.5 (deep molecular response: DMR ) at 12 months. All post‐treatment factors at 3 months predicted DMR by univariate analysis. However, RR ‐ BCR ‐ ABL 1 3m 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 ‐ ABL 1 3m was found to be a more useful predictor of DMR than HT ‐ BCR ‐ ABL 1 and BCR ‐ ABL 1 IS .
