[Late appearing Philadelphia chromosome as another clone in a patient with myelodysplastic syndrome harboring der(5;12)(q10;q10) at diagnosis].

: A 61-year-old man was referred to our hospital for leukocytosis and thrombocytopenia. Bone marrow examination showed hypercellular bone marrow accompanied by dysplasia, and the karyotype of his bone marrow cells was 46,XY, der(5;12)(q10;q10), +mar,inc[3]/46,XY[12]. A diagnosis of myelodysplastic syndrome, unclassifiable, was made. Analysis of major BCR/ABL1 chimeric RNA by real-time polymerase chain reaction method was positive, and then Ph chromosome was observed afterward. His Ph chromosome was seen in der(5;12)-negative cells analyzed by FISH, which suggested the late-appearing Ph chromosome evolved into another clone. Despite treatment containing imatinib, hydroxyurea, and cytosine arabinoside, he died due to respiratory dysfunction 5 months after the initial diagnosis. The autopsy revealed massive pulmonary infiltration by Ph-negative cells, suggesting MDS-derived clones. It has been reported that the late appearance of Ph chromosome associates with leukemic progression. Although the incidence of late-appearing Ph chromosome is estimated to be relatively low, further accumulation of cases is necessary for the evaluation of its impact on prognosis and disease progression.