Incidence and prognostic relevance of CD34 expression in acute myeloblastic leukemia: analysis of 141 cases

In 141 adult patients with diagnosis of acute myeloid leukemia the overall expression and intensity of expression of CD34 antigen on leukemic cells was investigated. Myeloid blasts were tested by applying direct immunofluorescence staining using anti-CD34 fluorescein monoclonal antibody in flow cytometry. CD34 antigen was found in 73 out of 141 (51%) cases and in particular in M0, M1 and M4 French-American-British (FAB) cytotypes, while M3 and M5 cases were rarely positive. In patients whose blasts expressed CD34 antigen a significantly lower rate of complete remission (CR) was observed as opposed to CD34 negative cases (61% vs 88%) (P = 0.001). Furthermore, a negative correlation between high intensity of CD34 expression, measured as a mean fluorescence index (MFI), and CR rate was observed. In particular, patients with a higher CD34 fluorescence intensity (MFI > 23), showed a further reduction in CR rate (48%). Also, these patients had a significantly lower overall survival (P = 0.03) as compared to patients with no expression of CD34 and patients with CD34 MFI < 23. In conclusion, these findings confirm that CD34 expression is frequently associated with "immature" FAB cytotypes (M0, M1 and M4) and with a reduced probability to achieve CR. Furthermore, a high CD34 intensity of expression should be considered as a reliable poor prognostic factor.