A biphenotypic transformation of 8p11 myeloproliferative syndrome with CEP1/FGFR1 fusion gene

We describe here the first case of 8p11 myeloproliferative syndrome (EMS) with t(8;9)(p11;q33), who unusually demonstrated B-lymphoblastic/monoblastic biphenotypic transformation. A 57-year-old woman was admitted because of leukocytosis and diagnosed as EMS. Bone marrow was infiltrated with myeloperoxidase (MPO)-, CD10+, CD19+, CD20+, CD34+, HLA-DR+ small lymphoblasts and MPO+, CD2+, CD4+, CD13+, CD14+, CD33+, HLA-DR+ large monoblasts. The karyotype was 46,XX,t(8;9)(p11;q33)20 and the CEP1/FGFR1 fusion transcript between CEP1 exon 38 and FGFR1 exon 9 was detected. This case clearly indicates that the blastic transformation in EMS with t(8;9) could arise in the stem cells, which differentiate into not only myelomonocytic but also B-lymphocytic lineages.