To that end, in the present report we evaluate a wide range of well known and widely validated oxidative stress parameters (lipid peroxidation, protein oxidation, and total antioxidant capacity), as well as non-enzyme (GSH) and enzyme (SOD, CAT, and GPx) antioxidant defense systems in the SLN of women with breast cancer determined as negative, with micrometastases, or with macrometastases by the OSNA method. The gene discussed is CAT; the disease is breast carcinoma.