OBJECTIVETo compare the immunophenotypic and clinical characteristics between NPM1 mutated acute myeloid leukemia (AML) (NPM1m(+)AML) and unmutated AML(NPM1m(-)AML) not otherwise characterized (NOS) under similar FAB subtypes constituent ratio.

METHODSImmunophenotyping and NPM1 gene mutation type-A, B and D and other leukemic related fusion genes were detected by multiparameter flow cytometry and real time RT-PCR or PCR, respectively. 104 AML patients with NPM1m(+)AML and performed immunophenotyping assay were included, 97 with NPM1m(-)AML.

RESULTSThere were significant difference between the two groups at presentation in terms of sex, white blood count(WBC), platelet counts (PLT), blast ratio, normal karyotype ratio, WT1 expression level, FLT3-ITD mutation positive rate and remission rate of first course of induction therapy (P < 0.05). On the immunophenotype, the expression of early differentiation antigens (CD34, HLA-DR, CD117, CD38), lymphocytic antigens (CD7, CD4, CD19, CD2), myeloid and monocytic differentiation-associated antigens (CD13, CD14, CD15) were lower, and that of CD33 as well as CD123 were higher in NPM1m(+)AML patients. Among them, only CD34, HLA-DR, CD7, and CD4 positive cases were significantly lower in NPM1m(+)AML group than in NPM1m(-)AML group (P < 0.05), the rest of them had significant difference in the number of positive cells (P < 0.05). Above features were further analyzed between the M1/M2 and M4/M5 subgroups. M1/M2 cases retained the women prominent and had a higher WT1 expression level (P < 0.05). The expression of monocytic differentiation-associated antigens including HLA-DR and lymphocytic antigens were higher and that of CD117 were lower in M4/M5 subtype (P < 0.05). Among them, the positive rates of HLA-DR, CD64, CD11b, CD10, CD15, and CD4 were significantly higher in M4/M5 than in M1/M2 in NPM1m(+)AML group (P < 0.05).

CONCLUSIONThe most clinical characteristics in NPM1m(+)AML patients are consistent with reports, but some immunophenotype are different to the previous reports under similar FAB subtypes constituent ratio. The major immunophenotypic features of NPM1m(+)AML patients are lower expression of progenitor, myeloid and lymphoid lineage antigens. Monocytic differentiation-associated antigens are only higher expression in M4/M5 cases when comparison with M1/M2 cases within NPM1m(+)AML group.