Successful treatment of Philadelphia chromosome-positive mixed phenotype acute leukemia by appropriate alternation of second-generation tyrosine kinase inhibitors according to BCR-ABL1 mutation status

Philadelphia chromosome-positive mixed phenotype acute leukemia (Ph⁺MPAL) is a rare type of acute leukemia having myeloid and lymphoid features. In the present study, we describe the successful treatment of a 71-year-old Japanese female patient with Ph⁺MPAL by the alternation of second-generation tyrosine kinase inhibitors according to BCR-ABL1 mutations. The patient survived in her third complete remission (CR) for over 4 years. In her first CR, the patient was treated with multiple-agent chemotherapy and underwent maintenance therapy with imatinib and monthly vincristine and prednisolone (VP). At the first relapse, an examination of the bone marrow revealed a transformation into acute lymphoblastic leukemia and an F317L mutation in BCR-ABL1 gene, which responded preferentially to nilotinib over dasatinib. She achieved second CR, and nilotinib with VP therapy was selected for maintenance treatment. At second relapse, BCR-ABL1 mutational analysis revealed Y253H mutation instead of F317L mutation, resulting in resistance to nilotinib. The patient achieved third CR with dasatinib and VP therapy, and maintained CR with this treatment. This suggests that appropriate alternation of TKIs may contribute to long-term survival in elderly patients with Ph⁺MPAL.