Clinical Relevance of Circulating Myeloperoxidase (MPO) in Acute Myeloid Leukemia (AML) and Myelodysplastic Syndrome (MDS).

MPO, a hemoprotein expressed in polymorphonuclear neutrophils and their precursors, is an important component of the antimicrobial activity of phagocytes and is associated with inflammatory response. Cellular expression levels of MPO, assessed by cytochemical staining, are used extensively for the diagnosis and subtyping of various leukemias. However, the association of circulating (plasma or serum) MPO levels with hematologic values and clinical outcomes of AML and MDS has not been reported. We investigated whether MPO, presumably released from leukemic cells, can be detected in the plasma of patients with AML and MDS. We further assessed the association of plasma MPO levels with hematologic characteristics and outcomes. 144 patients with AML, 28 patients with MDS, and 100 control subjects were included in the analysis. Patients with AML (median 19.3, range 1.0–9514.7 ng/mL) and MDS (median 13.6, range 1.0–3021.9 ng/mL) had significantly higher plasma MPO levels than control subjects (median, 4.9; range, 3.5–20.6 ng/mL). Because MPO levels and overall survival did not differ significantly between AML and MDS patients, the 2 groups were considered together in subsequent analyses. MPO levels were inversely correlated with overall survival (Cox regression analysis, P<0.001). In the multivariate model, the inverse correlation between MPO levels and survival was independent of cytogenetics, performance status, anticident hematologic disease (AHD), age, and diagnosis (AML vs MDS). Response to therapy in AML and MDS patients was not associated with plasma MPO levels. However, responders with high MPO levels had shorter remission duration (CRD), although this difference did not reach statistical significance (P = 0.07). As expected, MPO levels correlated with the level of differentiation of leukemic cells (FAB subclassification): patients with M0 and M6 had lower MPO levels than those with M2, M3, or M4 (P = 0.0001). MPO levels also correlated positively with white cell count, beta2-microglobulin, monocyte, LDH, BUN, and creatinine levels. These data indicate that plasma MPO levels are elevated in AML and MDS and may be useful as a prognostic factor. Our findings also raise the question of how the proinflammatory properties of MPO might affect the clinical course of these diseases.