Which stain is positive in acute myeloid leukemia, associated with M2 type?

In acute myeloid leukemia (AML), specifically the M2 subtype, myeloperoxidase (MPO) staining is a crucial diagnostic tool. Myeloperoxidase is an enzyme found in myeloid cells, and its presence indicates the differentiation of these cells towards the granulocytic lineage. In cases of M2 AML, where there is a predominance of myeloid blasts that often retain some ability to differentiate into neutrophils, a positive myeloperoxidase stain reflects this characteristic.

The positive reaction indicates that the leukemic cells have retained their myeloid characteristics, and thus, the identification of this specific enzyme helps confirm the diagnosis of AML M2. The successful staining suggests that the blast cells are capable of synthesizing this enzyme, reinforcing the understanding that M2 allows for a degree of maturation, distinguishing it from other subtypes that may not show this enzyme.

This staining technique is significant in the diagnostic process, helping to differentiate AML from other leukemias such as acute lymphoblastic leukemia, where myeloperoxidase would typically be negative.