Acute myeloid leukemia presenting with an unusual phenotype

The diagnosis of acute myeloid leukemia (AML) requires expression of myeloid markers, CD13 and 33, positivity for myeloperoxidase and/or anti-MPO. AML with an unusual phenotype represented by myeloperoxidase positivity and absence of myeloid antigen expression is seen in less than 10% of cases. Myeloid antigens may be detected in the cytoplasm where they may be present before they are expressed on the cell surface.

Here we present two rare cases of AML where the blasts were positive for myeloperoxidase and anti-MPO but negative for surface CD13 and CD33. Although AML-M2 with t(8; 21) is the subtype usually seen in these cases, one of our patients had biphenotypic leukemia with del⁹