Acute Erythroid Leukemia: A Distinctive Subtype of AML? Outcome and Prognostic Factors in Comparison with Non-M6 AML. The Gimema Experience.

Erythroleukemia is characterized by a peculiar marrow feature: a proliferation of erythroblasts greater than 50% and of myeloblasts greater than 30%, according to the FAB classification.

Treatment strategies are usually indistinct from other forms of acute myeloid leukemia (AML), with the exception of acute promyelocytic leukemia. Although generally considered as a very aggressive subtype of AML, very few data are available concerning epidemiologic features and specific outcome of erythroleukemia among AMLs.

Adult patients with AML consecutively enrolled in the GIMEMA trials AML10 and LAM99p were retrospectively analyzed with the aim of evaluating the epidemiologic features and outcome of acute erythroid leukemia (FAB M6) characterized by morphological/cytochemical criteria after central revision, in comparison with non-M6 AML.

Among 1675 AML patients, 59 (3.6%) were identified as M6; 39 were males and 20 females, the median age was 49 years (range 25.9-60.8), the median WBC count at diagnosis 2.7 × 10⁹/l (range 0.7-41.8), the median Hb level 7.8 gr/dl (range 5.1-11.8) and the median platelet count 38 × 10⁹/l (range 6-245).

Univariate analysis showed a statistical difference between the M6 cases and the non-M6 series enrolled in these two clinical trials with regard to: incidence of male gender (p=0.03), prevalence of older age (p=0.001), leukopenia at diagnosis (p<0.0001), decreased levels of Hb (p=0.0006), lower platelet count (p=0.05), peripheral blast count (p<0.0001) and increased PMN count (p<0.0001). A previous myelodisplastic phase was reported in 5.6% of M6 cases compared to 1.7% in the other AML subtypes (p=0.07).

Analysis of response to intensive chemotherapy, evaluated as ITT, showed that 64.4% of M6 patients achieved a complete remission (CR) compared to 69.6% in the other FAB subtypes (p=0.39); a similar induction death rate (13.5%) was observed in both groups.

Overall survival (OS) at 60 months was 29.5% in M6 patients and 34% in the other FAB types (p=0.75), as shown in the figure; no significant difference was recorded also with regard to disease-free survival (DFS): 44% in M6 vs 39.7% in the other FAB types after 60 months of follow-up (p=0.59). For patients who obtained a CR, the cumulative incidence of relapse (CIR) showed no statistical differences: 45% at 60 months in M6 vs 46.9% in the other types, p=089). Also the cumulative incidence of non-relapse mortality (CINRM) at 60 months was similar in both groups: 10.7% in M6 vs 13.4% in the other types, p=0.62.

Despite the higher incidence of some risk factors - higher age, higher proportion of myelodisplastic pre-phase and cytopenias - in this rare form of AML the CR duration and the OS are similar to those observed in the other more frequent forms of AML. Based on this analysis, the prognosis of this form of acute leukemia does not differ from that of the other subtypes.

No relevant conflicts of interest to declare.