南予医学雑誌　第18巻

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南予医誌　Vol.18　No. １　2017－76－IntroductionMixed-phenotype acute leukemia（MPAL）accounts for 1.6-2.4％ of acute luekemias and is classified as one of five subtypes of ambiguous acute leukemias in the 2016 World Health Organization（WHO）Classi-cation of Tumours of Haematopoietic and Lymphoid Tissues１）．Diagnosis of MPAL is based on evidence that 20％ or more of the leukemic cells in bone marrow are posi-tive for both myeloid and lymphoid mark-ers， according to the WHO diagnostic crite-ria revised in 2008２，３）．The t（９：22）（ｑ34.1；ｑ11.2）chromosome aberration， known as the Philadelphia chromosome（Ph）， is the most common genetic abnor-mality in MPAL， accounting for 25％ of cases１）．Although no standard therapeutic approach has yet been established for el-derly patients aged 65 years and older with newly diagnosed Philadelphia chromosome-positive（Ph＋）MPAL， some reports have indicated that the BCR-ABL tyrosine kinase inhibitor（TKI）imatinib， or a second-gen-eration TKI such as dasatinib or nilotinib plus chemotherapy， are effective in this setting４-６）．When cytotoxic chemotherapy is used， physicians need to adjust the regi-men intensity according to patient age， performance status， and comorbidities， as there is no standard chemotherapy for el-derly patients．However， the effectiveness of TKIs is limited because patients show a short response duration， due mainly to mu-tations in the BCR-ABL tyrosine kinase do-main（TKD）， including T315I mutation ７，８）．Hence， a new treatment strategy for these patients is necessary in order to overcome this limitation．Ponatinib is a third-generation TKI report-edly active against both wild-type BCR-ABL and most of the clinically significant BCR-ABL TKD mutations， including T315I mu-tation， in chronic myeloid leukemia （CML）and Ph＋ acute lymphoblastic leukemia（ALL）９）．Some reports have suggested that ponatinib， alone or in combination with chemotherapy， is highly effective for patients with newly diagnosed and relapsed Ph＋ ALL９，10）．However， little is known about the efcacy and safety of ponatinib in Ph+ MPAL patients resistant or intolerant to other TKIs．Here we report an elderly patient with relapsed MPAL who suffered severe adverse effects of dasatinib but was treated successfully with ponatinib and prednisolone．Case PresentationA 74-year-old man with a history of hyper-tension was found to have an elevated WBC count during a routine health examination and was referred to us in October 2015．The results of a clinical examination were normal， but a complete blood cell count revealed a WBC count of 15270 /μL with 14.0％ lymphoblast-like cells， with a nor-mal hemoglobin level and platelet count．A bone marrow specimen demonstrated small lymphoblast-like cells， accounting for 46.6％ of nucleated cells（Fig.１）．Cyto-chemical staining showed that these cells were positive for myeloperoxidase（MPO）