Prognostic factors and treatment effects on survival in acute myeloid leukemia of M6 subtype: a retrospective study of 54 cases.

Background: Since 1976, erythroleukemia has been included within the FAB classification system of acute myeloid leukemia (AML) which designates it as M6 AML. This report describes the data of 54 patients with newly diagnosed M6 AML, consecutively seen in our hospital between May 1976 and May 1999. Patients and methods: There were 40 males and 14 females. Median age was 59 years. Pancytopenia was the most common feature at diagnosis. Twenty-six percent of cases presented with secondary AML. Karyotype was successfully performed in 35 cases. Eleven patients presented with normal karyotype, nine with simple karyotypic abnormalities, and fifteen with major karyotypic abnormalities. Fifty of the fifty-four patients received one or two courses of induction chemotherapy combining anthracyclines with cytarabine according to different successive protocols. One elderly patient only received low-dose cytarabine, and three patients died before any chemotherapy could be given. Results: Complete remission (CR) was achieved in 29 cases (54%, 95% confidence interval (CI): 40%-67%). As post-remission therapy, four patients could be allografted, and two underwent autologous transplantation. All other treated patients received continuation chemotherapy. Twenty-one patients have relapsed (72%). Median time to relapse was six months. Among those patients, only eight achieved a second CR (38%). The median disease-free survival (DFS) was eight months (95% CI: 4-10 months) with a five-year survival rate of 17%. Median overall survival (OS) was nine months (95% CI: 5-12 months) with a five-year survival rate of 13%. In univariate analysis, poor prognostic factors for DFS were secondary AML (P = 0.05) and initial platelet count < 50 x 109/l (P = 0.02). Poor prognostic factors for OS were age greater than or equal to 60 years (P = 0.005), secondary AML (P = 0.05), initial 'blastic' fever (P = 0.0004), and initial haemoglobin level < 90 g/l (P = 0.03). All factors, but haemoglobin level, remained significant in the multivariate analysis. Although it was not statistically significant, there was a trent for a better prognosis of M6 patients presenting with normal karyotype as compared to those displaying chromosomal abnormality. Conclusions: This retrospective analysis points to a somewhat heterogenous group of AML in terms of clinical and biological features, and outcome. Distinctive subgroups can be identified according to prognostic factors related to survival. A larger multicenter study with well-defined diagnostic criteria is warranted to further clarify treatment effects.