Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the BCR-ABL1 fusion gene and accounts for approximately 15–20% of all leukemias. While the majority of cases harbor the p210 (major) transcript, the p190 (minor, e1a2) transcript is exceedingly rare, representing only about 1–2% of CML cases. This subtype may exhibit distinct hematologic features compared to p210-positive cases, particularly peripheral monocytosis and marked splenomegaly. In the literature, responses to tyrosine kinase inhibitor (TKI) therapy in p190-positive CML have been reported to be variable, and long-term outcomes are described only in limited case reports. Therefore, presenting the clinical and laboratory features of this uncommon subtype is of particular importance.

A 23-year-old female patient presented with complaints of fatigue and dyspeptic symptoms. Complete blood count revealed WBC: 70 × 10³/µL, neutrophils: 58.5 × 10³/µL, monocytes: 7.38 × 10³/µL, hemoglobin: 10.4 g/dL, and platelets: 871 × 10³/µL. Abdominal ultrasonography demonstrated splenomegaly with a longitudinal diameter of 175 mm. Peripheral blood smear and bone marrow aspiration-biopsy findings were consistent with chronic myeloid leukemia, with blasts reported as <5%, and the overall evaluation was described as a “myeloproliferative neoplasm.”

Molecular testing showed negative results for the major BCR-ABL1 transcript, whereas the minor BCR-ABL1 (e1a2) transcript was detected at 3.4%. The patient was started on first-line therapy with imatinib. At the third month of treatment, BCR-ABL1 (minor) was 10.51%, although hematologic parameters had improved. With continuation of imatinib, the sixth-month evaluation showed a decrease in BCR-ABL1 (minor) to 1.56%, with a normalized blood count (WBC: 5.31 × 10³/µL, Hb: 10.6 g/dL, platelets: 226 × 10³/µL). The patient’s clinical symptoms had resolved, and she remains on imatinib therapy with ongoing follow-up.

While the p210 (major) transcript is the most frequently detected form in chronic myeloid leukemia (CML), the p190 (minor, e1a2) transcript is exceedingly rare, occurring in only about 1–2% of cases. In the literature, this subtype has been associated with peripheral monocytosis and marked splenomegaly, and responses to tyrosine kinase inhibitors (TKIs) have been reported as variable. In some patients, imatinib therapy may not achieve sufficient molecular response, whereas deeper responses have been described with second-generation TKIs.

In our patient, early hematologic response was achieved with imatinib, and by the sixth month a marked molecular reduction was observed. Through this case, we aim to highlight the clinical and laboratory characteristics of p190-positive CML and to emphasize the importance of close molecular monitoring and careful evaluation of treatment response in this rare subtype.