Correlation of FLT3 mutations with expression of CD7 in acute myeloid leukemia

FLT3 mutations are common in acute myeloid leukemia (AML), particularly in cases with normal karyotype. Internal tandem duplication (ITD) and also point mutations affecting aspartic acid 835 (D835) are reported. A previous study demonstrated aberrant expression of CD7 on blasts in de novo AML cases with FLT3/ITD mutations. Our study goals are to expand the evaluation of this association to a larger group of patients; to evaluate the association of aberrant CD7 expression in AMLs with D835 mutation, not previously done; to evaluate if aberrant CD7 expression may serve as a surrogate marker for predicting FLT3 mutational status; to evaluate if combined FLT3 with NPM1 mutational status has a better correlation with CD7 expression. The FLT3 mutational analysis was performed on DNA extracted from 149 previously diagnosed AML cases with cytogenetics and flow cytometry evaluation available. Of 149 patients, 28 were positive for FLT3; CD7 was positive in 13 of 20 ITD-positive cases, 5 of 6 D835-positive cases, and 1 of 2 ITD/D835-positive cases. The association of CD7 positivity and FLT3 positivity was found to be significant. However, CD7 expression has a low positive predictive value of 30% and a negative predictive value of 90%. Because of the low positive predictive value, CD7 expression cannot be used as a surrogate marker for FLT3 positivity; even though the negative predictive value is higher, some cases that are FLT3 positive may be missed if CD7 expression would be used for screening.