A total of 777 patients have been enrolled in our nested case-control study. 293 of them operated for breast cancer (cases) and 484 healthy women (controls) have been recruited between 2008 and 2009 to take part to our study for evaluating the association between MS and breast cancer. Liver or renal disease, thyroid pathology and coronary artery disease were considered exclusion criteria. After obtaining informed consent, signing the authorization to be enrolled in the study, for each woman anthropometric features were measured, including weight in kilograms, height in meters, waist and hip circumference, arterial blood pressure was taken and venous blood was collected [15]. BMI (kg/m²) was calculated from weight and height values according to World Health Organization classification (< 25 kg/m²= underweight/normal, ≥ 25 kg/m²= overweight/obese), waist and hip ratio (WHR) was obtained from waist and hip circumference, measuring the smallest circumference of both to discriminate between android and gynoid fat distribution [22]. From blood samples fasting plasma glucose, HDL-C, triglyceride, uric acid, insulin and testosterone levels were assessed. Fasting plasma glucose, HDL-C and triglyceride were measured according to NCEP ATP III criteria. The normal range for uricemia was 2.6-6.0 mg/dl. Insulin levels were defined in normal range when between 5 and 25 mcU/ml, whereas ≥ 25 mcU/ml were considered hyperinsulinemia. Testosterone levels were considered in the normal range when 0.20-1.20 ng/ml. Levels > 1.20 ng/ml were considered indicative of hyperandrogenic status. Women were asked to answer a questionnaire about chronic diseases, tobacco use, alcohol abuse, food intake, physical activity grade, parity, age of menarche, menopausal status, oral contraceptive use, hormonal therapy use, personal and familial history of cancer. According to the NCEP ATP III [10], women presenting three disorders were diagnosed with low grade MS [5], whereas women presenting more than three disorders (four or five) were diagnosed with high grade MS. Chi-squared test and logistic regression analyses (OR and 95% CI) were used to confirm the association between MS and breast cancer and to calculate the risk. Statistical significance was considered at P < 0.05.