Myelodysplastic syndrome preceding acute myelomonocytic leukemia with dysplastic marrow eosinophilia and inv(16).

A 44-year-old Japanese male having refractory anemia with excess of blasts (RAEB) preceding acute myelomonocytic leukemia (AMMoL) with dysplastic marrow eosinophilia (M4Eo in the FAB classification) is reported. Sequential cytogenetic studies revealed a specific chromosomal abnormality, inv(16) (p13q22), when RAEB was first diagnosed and again when overt leukemic transformation compatible with M4Eo was manifested. However, during the interval between the RAEB and AMMoL, an unrelated abnormal karyotype without inv(16), 47,XY,+9, was seen, when hematological data revealed remission after a low dose of cytosine arabinoside was administered. In this patient eosinophils in the marrow were involved in the leukemic process cytogenetically, because a few metaphases overlaid with eosinophilic granules had the inv(16) with other numerical abnormalities.