Cytogenetic heterogeneity in erythroleukemia defined as M6 by the French-American-British (FAB) Cooperative Group criteria.

Chromosomal banding studies were performed on 10 patients diagnosed as having the M6 subtype of acute nonlymphocytic leukemia (erythroleukemia) according to the French-American-British (FAB) Cooperative Group criteria revised in 1985. Five patients had complex karyotypic abnormalities consisting of three or more defects, four of the five had deletion 7q, and three of the four had monosomy 5 or deletion 5q; the other five patients had normal karyotype. The patients of the former group had significantly higher white blood cell and blast cell counts in the peripheral blood and a higher serum lactate dehydrogenase level than the patients of the latter group. The progress of the disease in the former group was aggressive, resulting in a very poor prognosis. In contrast, the patients in the latter group had a relatively stable clinical course, resulting in a significantly longer survival. Furthermore, erythroblasts of all the patients with normal karyotype were negative or at most weakly positive to periodic acid-Schiff reaction, whereas the cells were strongly positive in three of five patients with complex defects. Accordingly, we suggest that M6 subtype is cytogenetically heterogeneous, and that chromosomal findings are a useful prognostic indicator of this disorder.