Elevated circulating levels of MPO were detected in breast cancer patients treated with anthracyclines (n = 192) as part of the CECCY trial with 1.3- and 1.5-fold increase at 3 months (17.7 ng/mL (11.1, 31.1)) and 6 months (19.2 ng/mL (11.1, 37.8)) after initiation of treatment, respectively, compared to the baseline (13.2 ng/mL (7.9, 24.8)). Here, MPO is linked to breast carcinoma.