TO THE EDITOR: A 38-year-old man with history of corrected rheumatic heart disease was incidentally diagnosed with BCR-ABL1-positive chronic myeloid leukemia (CML). He was treated with imatinib 400 mg/day, with which he achieved major molecular remission (MMR) after 12 months of therapy. He was followed up regularly with examinations of complete blood counts and 6-monthly quantitative BCR-ABL1 transcript levels, which improved to MR4.5 in 24 months. After 4 years of regular treatment with good drug compliance, he showed loss of MMR on routine testing with increased BCR-ABL1/ABL1 transcript levels of up to 32.4% on the international standard (IS) scale. Hemogram showed hemoglobin level of 68 g/L, leukocyte count of 4.6×10⁹/L, and platelet count of 202×10⁹/L. Peripheral blood film (PBF) showed leukoerythroblastic picture with eosinophilia (13%), basophilia (10%), and significant dysgranulopoiesis (Fig. 1A–C). Bone marrow was markedly hypercellular with 4% blasts, marked dysgranulopoiesis, dysmegakaryopoiesis (>90% dwarf forms) (Fig. 1D, E), eosinophilia (16%), and basophilia (9%). This morphology was consistent with a loss of hematological responses. Conventional cytogenetics revealed 49,XY,+8,t(9;22)(q34;q11.2),i(17)(q10),+der (22)t(9;22)(q34;q11.2). Fluorescent in situ hybridization (FISH) using the Vysis BCR/ABL1/ASS1 Tri-Color Dual Fusion Probe and TP53/CEP17 dual colour Probe (Abbott Molecular, Abbot Park, IL, USA) confirmed the presence of an additional Philadelphia chromosome and loss of one copy of TP53 gene in concordance with isochromosome 17q (Fig. 1F, G). In a patient who previously achieved MMR, these cytogenetic abnormalities suggest clonal evolution and hence are consistent with accelerated phase of CML. In view of secondary resistance to imatinib therapy, ABL kinase domain mutation analysis by Sanger sequencing was performed, which did not reveal any mutations. He was subsequently administered dasatinib 100 mg daily. However, after 2 weeks of treatment, the patient developed symptoms of fluid overload and heart failure attributed to dasatinib. The dose of dasatinib was then decreased to 50 mg daily, which was well tolerated. The patient showed normalization of counts, and the 3-month quantitative BCR-ABL/ABL ratio was 3.4% IS (target <10%). However, he continued to show granulocytic dysplasia in PBF. FISH revealed BCR-ABL positivity and additional signals consistent with extra Philadelphia chromosomes in 90% of the cells. Dysplasia, although not a recognized criterion, has been previously reported as a characteristic feature of accelerated phase of CML [12]. Even in the era of molecular monitoring, a careful morphological evaluation of PBF continues to be important when accelerated phase of CML is suspected, and further confirmatory tests, such as chromosome studies, should be performed for early diagnosis and subsequent timely treatment. The inclusion of dysplasia as a surrogate marker of clonal evolution should be further investigated in larger studies.