Lymph Nodes, Mixed phenotype acute leukemia, MPO stain

Acute leukemia of ambiguous lineage includes leukemia with no lineage-specific antigens (acute undifferentiated leukemia, AUL) and those with blasts that express antigens of more than one lineage (mixed phenotype acute leukemias, MPAL). The diagnosis rests on immunophenotyping, preferably via flow cytometry but may also be established by immunohistochemistry as.

Mixed phenotype acute leukemia, T/myeloid, accounts for less than 1% of leukemias. It is characterized by a dimorphic blast population that meets the criteria for both T-lymphoid and myeloid lineage. In this case, the dual population of atypical cells shows striking compartmentalization. The atypical monocytoid blastoid population occupies the sinuses and parasinusoidal regions (as highlighted by MPO), whereas, the atypical lymphoid blastoid population infiltrates the remaining parenchyma (as highlighted by TdT).

Prognosis is poor, although data on outcomes is limited. There is controversy regarding which component of the leukemia to direct therapy against: myeloid, lymphoid, or both.

This slide shows MPO stain. See related content for H&E and TdT stains.