Metastasis is the leading cause of cancer death. Considering that lymph nodes are the major pathway for cancer spreading and that the metastatic process is under oxidative stress effects, this study aims to evaluate the differential lipid peroxidation profile in the blood of breast cancer patients regarding their lymph nodal status (LN). A total of 105 women diagnosed with breast cancer were included before chemotherapy started. LN was determined by assessing the histopathological analysis of patients' biopsies, and groups were categorized according to the presence (LN+