BCR: : ABL1-Positive Secondary B-Acute Lymphoblastic Leukemia Mimicking Acute Megakaryoblastic Leukemia Following Multiple Myeloma

A 63-year-old woman was diagnosed with IgG-kappa Multiple myeloma (MM) in January 2021, confirmed by 71% abnormal plasma cells on bone marrow smears (Fig. 1a-b) and aberrant plasma cells with CD45CD19CD38CD138BCMAkappalambdaphenotype by flow cytometry.She received bortezomib and lenalidomide-based regimens followed by allogeneic hematopoietic stem cell transplantation (HSCT) in July 2021 and lenalidomide maintenance from September 2022.The patient remained in remission until January 2025, when she developed fatigue and dizziness.Bone marrow smears revealed 76% blasts with medium to large cell size, irregular nuclei, and basophilic cytoplasm with occasional cytoplasmic blebbing or pseudopod formation, resembling megakaryoblastic morphology (Fig. 1c-d).Myeloperoxidase staining was negative.Flow cytometric analysis revealed 71% blasts were positive for CD10, CD19, CD22, CD99, cCD79a, HLA-DR, CD38(partial), CD13(partial), CD33(partial), and CD7(partial), and negative for cCD3, MPO, CD34, CD117, CD4, CD56 and CD41.Quantitative reverse transcription polymerase chain reaction identified BCR::ABL1 p190 transcript.Karyotyping revealed t(9;22)(q34;q11)[10]. Next-generation sequencing detected no additional mutations.Given the history, a diagnosis of secondary Philadelphia chromosome-positive (Ph+) B-ALL with BCR::ABL1 fusion following MM was made.She was initiated on vincristine-prednisone chemotherapy combined with flumatinib, a second-generation