Diagnosis and characterization of acute erythroleukemia subsets by determining the percentages of myeloblasts and proerythroblasts in 69 cases

Acute erythroleukemia (FAB M6) is a rare heterogeneous disease with an incr ease in red cell precursors and myeloblasts. Three subsets have been descri bed: M6A (myeloblast-rich erythroleukemia); Men (proerythroblast-rich eryth roleukemia); and M6C (myeloblast-and proerythroblast-rich mixed variant). T his study was undertaken to define and compare the clinical courses and sur vival outcomes among M6A, M6B, and M6C variants of erythroleukemia, Sixty-n ine cases of M6 leukemia were categorized as consisting of greater than or equal to 50% erythroid of all nucleated cells and M6A with greater than or equal to 30% myeloblasts/nonerythroid component; M6B with greater than or e qual to 30% proerythroblasts/erythroid component; and M6C with greater than or equal to 30% myeloblasts and greater than or equal to 30% proerythrobla sts. The demographics, cell type distribution, and survival (mean +/- sd) o f these groups were compared. There were 32 M6A, 26 M6B, and 11 M6C patient s. No significant difference was seen among the groups in age, sex, or trea tment. Compared to M6A, both the M68 (P < 0.0001) and M6C (P < 0.0001) vari ants showed a statistically significant increase in the percentage of bone marrow erythroid cells, proerythroblasts, and the proerythroblasts/erythroi d ratios. Comparing the groups for survival, M6B (3 +/- 3.6 months) versus M6A (25 +/- 28 months), P < 0.002, and M6C (10 +/- 13 months) versus M6A, P < 0.01 had a poorer prognosis. Calculating the proerythroblasts as a compo nent of total bone marrow erythroids provides a complimentary method for de lineating the pure red cell erythroleukemia (M6B) and mixed variant (M6C), similar to that for the myeloid/erythroid (M6A) leukemia. Now that it is po ssible to delineate erythroleukemia subtypes, innovative treatments are ind icated to target the malignant erythroid population, which is resistant to myeloid-based therapies. (C) 2000 Wiley-Liss, Inc.