Acute myelomonocytic leukemia (M4) with eosinophilia: problems concerning chromosome 16 abnormality

A case of acute myelomonocytic leukemia is reported which was hematologically classified as M4 (FAB), because the patient had a high count of immature eosinophils with typical histochemical features in the bone marrow. An abnormal chromosome #16 was found besides a trisomy 22 or a monosomy 18 in part of the cultured bone marrow cells and unstimulated blood cells but not in directly prepared bone marrow. The structural aberration of chromosomes #16, which was demonstrated best by CBG-banding, was more likely due to a partial deletion of the long arm than to an inversion. The difficulties involved in correct cytogenetic diagnosis of such cases are discussed.