Concurrent Chronic Myeloid Leukemia and Chronic Lymphocytic Leukemia at Initial Presentation: A Case Report and Review of the Literature.

Introduction: Concurrent chronic myeloid leukemia (CML) and chronic lymphocytic leukemia (CLL) in the same patient are rare and may be overlooked when leukocytosis is attributed to a single hematologic process. We report a case of synchronous CML and CLL identified at initial presentation, highlighting the diagnostic value of integrating morphology, immunophenotyping, cytogenetics, and molecular testing. Case Presentation: A 44-year-old man presented with progressive weight loss and back pain and was found to have leukocytosis with neutrophilia, absolute lymphocytosis, eosinophilia, and basophilia. Peripheral blood smear and flow cytometry supported CLL, whereas reverse-transcription polymerase chain reaction and cytogenetics demonstrated e13a2 BCR::ABL1 and t(9;22)(q34;q11.2), confirming concomitant CML in chronic phase. Bone marrow examination showed hypercellularity with granulocytic hyperplasia and nodular lymphoid infiltrates, and fluorescence in situ hybridization detected 13q14.3 deletion in the lymphoid clone. Imatinib 400 mg daily was initiated but was replaced with dasatinib 100 mg daily because of intolerance. At 14 months of follow-up, the patient remained clinically stable on dasatinib, with early molecular response at 3 months and major molecular response at 12 months, while the CLL remained under observation without indication for CLL-directed therapy. Conclusion: This case highlights the diagnostic complexity of synchronous hematologic malignancies and the importance of comprehensive multimodal evaluation when clinical, morphologic, and laboratory findings are not fully explained by a single diagnosis. Treating the clinically dominant clone while monitoring the second clone may be appropriate when the latter is asymptomatic.