Extra

mpo (myeloperoxidase)

An indicator of granulocytic maturation that in acute leukaemia is highly specificity for the diagnosis of aml. expression should not be observed in typical all but mpo can contribute to a diagnosis of mixed-phenotype acute leukaemia mpal. note that although specific for aml expression may not occur on more primitive aml forms or where maturation is non-granulocytic e.g. monocytic erythroid or megakaryocyte lineages

normal function and expression

myeloperoxidase is a lysosomal enzyme that produces hypochlorous acid from hydrogen peroxide during the neutrophil neutrophil respiratory burst these reactive compounds are used by the neutrophil to kill pathogens. mpo is present in neutrophils and eosinophils at all stages of maturation and developing basophils. mpo staining is seen in monocytes but at low intensity. erythroid precursors and lymphocytes are mpo-negative.

what is its diagnostic role

• as a diagnostic antibody in aml expressed in around 60% of aml cases generally those with granulocytic maturation weakly expressed by promonocytes. *in otherwise typical all a small number of mpo-expressing cells is allowed precise criteria vary but generally 5% In cases with mixed phenotype acute leukaemia mpal expression of mpo can alone be used to establish myeloid lineage

other relevant information technically enzymatic measures of mpo either mpo cytochemistry or sudan black b are probably least sensitive. flow cytometric detection of mpo has lower sensitivy than immunohistochemical detection on trephine this may be because ihc detects expression ofprecursor enzyme form of mpo as well as thefunctional form . if there is doubt about the level of expression then ich on trephine biopsies can be useful.

summary tables

expression by acute leukaemias and by haematogones rare pro-ball rare early pre-ball rare pre-ball rare ball rare pro-tall rare mature-tall mod aml * rare haemato-gones

• *inamlmpoishighly specific fordiagnosis butisnotdetected inallcases 2.

expression byb-lymphoproliferative disorders rare cll* rare pll rare mcl rare fl rare hcl rare hclv rare mzl rare lpl rare pcs