Circulating Myeloperoxidase (MPO) as a Tumor Marker in Patients with Chronic Myeloid Leukemia (CML).

MPO is a hemoprotein expressed in polymorphonuclear neutrophils and their precursors. Free circulating MPO in the plasma or serum is an important indicator of inflammation in various inflammatory diseases, whereas cellular expression levels of MPO, assessed by cytochemical staining, are used extensively for the diagnosis and subtyping of various leukemias. The role of circulating MPO levels in the evaluation of CML has not been assessed. In this study, we examined the association of plasma MPO levels with hematologic characteristics and clinical outcome in 107 patients with Philadelphia chromosome-positive CML: 74 in chronic phase (CP) and 33 in accelerated/blastic (ACC/BC) phase). 100 apparently healthy individuals were included as a control group. All patients received imatinib mesylate therapy, with a median follow-up period of 18.6 months (range, 2.1–31.1 months). Overall, MPO levels did not differ significantly between CP and ACC/BC patients (Wilcoxon test, P=0.34). However, both CP (median, 38.2; range, 4.9–11421.6 ng/mL) and ACC/BC (median, 47.00; range, 3.4–1423.6 ng/mL) groups had significantly higher levels than control subjects (median, 4.9; range, 3.5–20.6 ng/mL). Response rates were 77% for CP patients and 57% for ACC/CP patients. When both groups were considered together, nonresponders had significantly higher MPO levels than responders (P = 0.03). In separate analyses, this association held true for ACC/BC patients (P = 0.04) but not for the CP group. MPO levels correlated strongly with WBC, LDH, percent basophiles, and percent Philadelphia chromosome-positive metaphases (all P <0.001). These data suggest that plasma MPO levels are elevated in CML and may be useful in predicting response to imatinib mesylate therapy for patients in ACC/BC phase; whether the association of MPO levels with response reflects an underlying association with tumor burden requires further study. Longer follow-up with larger samples sizes may be needed to accurately evaluate the relationship between plasma MPO levels with response and overall survival for patients in CP.