The case of a 44-year-old Japanese woman diagnosed with mixed-phenotype acute leukemia with t(9;22)(q34.1;q11.2); BCR-ABL1 (MPAL-BA) is reported. Her white blood cell count was 5,100/μL with 13.0% blasts; positive for CD34, HLA-DR, MPO, CD33, CD19, cytoplasmic (cy) CD79a, CD22, CD10, and TdT; and negative for cyCD3. G-band cytogenetic analysis detected a normal karyotype. Fluorescence in situ hybridization detected BCR-ABL1 (9.0%) and a minor BCR-ABL1 mRNA at 4.2 × 10⁴ copies/µg RNA. The patient was treated with dasatinib monotherapy (140 mg daily). Bone marrow examination revealed cytogenetic remission (CyCR) with minor BCR-ABL1 mRNA detected at 1.1 × 10³ copies /µg RNA on day 31. No adverse events of dasatinib therapy were observed. MPAL-BA is very rare and dasatinib monotherapy efficacy for this diagnosis was previously unknown. The patient achieved CyCR with dasatinib monotherapy as first-line treatment. The present case suggests that dasatinib monotherapy may be effective and safe for MPAL-BA induction therapy.

mixed phenotype acute leukemia with t(9;22)(q34.1;q11.2), BCR-ABL1 translocation, mixed phenotype acute leukemia, BCR-ABL1, dasatinib