Abnormalities of chromosome 16 in association with acute myelomonocytic leukemia and dysplastic bone marrow eosinophils

Six patients with M4 acute myelomonocytic leukemia ( AMMoL ) were identified who had abnormalities of chromosome 16 in bone marrow cells. Five had a pericentric inversion, inv(16)( p13q22 ), and a sixth patient had a translocation, t(16;16)(p13.1;q22). Each of these six patients had bone marrow eosinophils that were abnormal in morphology on light and/or electron microscopy and by cytochemical stains. The eosinophils constituted 1%-24% of nucleated marrow cells. Of 61 acute nonlymphocytic leukemia (ANLL) patients, all those with AMMoL and abnormal bone marrow eosinophils had an inv(16) or a t(16;16). One other patient in this group had a rearrangement of chromosome 16 (with a break in the short arm at band p13); however, the ANLL type was M1 and no abnormal eosinophils were present. Four patients with ANLL types other than M4 had an increase in marrow eosinophils; three in whom the eosinophils appeared normal and one with ANLL-M2 and bizarre eosinophils morphologically distinct from those seen in AMMoL . Chromosome pair 16 was normal in the latter four patients. AMMoL with dysplastic bone marrow eosinophils appears to represent a unique clinicopathologic entity associated with several related abnormalities affecting 16q . The morphologic features of both blasts and eosinophils may be more important than the absolute number of eosinophils in the marrow in identifying this group of patients. This may have prognostic importance as five of six patients achieved complete remission with standard antileukemic therapy and are still alive.