Summary Epidemiological data suggest a close link between obesity and breast cancer, the most frequently occurring cancer in women. The metabolic syndrome is typically associated with abdominal obesity and comprises disturbances in glucose and/or lipid metabolism and/or hypertension. Recent studies have established a specific association between the metabolic syndrome - as well as its components - and breast cancer, indicating both an increased risk of developing breast cancer and a poorer prognosis. In premenopausal women, obesity might have a protective effect only on receptor-positive tumors, whereas a positive association was observed between obesity/abdominal obesity and an increased risk of triple-negative breast cancer (TNBC). Overall survival and disease-free survival were reported to be significantly shorter in premenopausal obese women with TNBC compared to non-obese women, but these results are still inconsistent and need further research. The metabolic syndrome is characterized by a state of insulin resistance/hyperinsulinemia and subacute chronic inflammation, with both conditions offering a plausible mechanistic link towards breast cancer. Thus, in addition to their increased risk of cardiovascular morbidity and mortality, women with this syndrome represent a group at elevated risk of developing breast cancer and with poorer prognosis.

Cohort trials have shown evidence that obesity and a low level of physical activity are not only associated with a higher risk of developing breast cancer, but also with an increased risk for recurrence and reduced survival in breast cancer patients. The SUCCESS C study is the first European trial to evaluate the effect of an intensive lifestyle intervention program on disease-free survival in women with early breast cancer and to examine the predictive value of selected biomarker candidates. A total of 3,547 women with early-stage, Her2/neu-negative breast cancer will be included. The first randomization will compare disease-free survival in patients treated with either 3 cycles of FEC (epirubicine, fluorouracil, cyclophosphamide), followed by 3 cycles of docetaxel or 6 cycles of docetaxel-cyclophosphamide, and thus assess the role of anthracycline-free chemotherapy. The second randomization compares disease-free survival in patients with a body mass index of 24–40 kg/m² receiving either a telephone-based individualized lifestyle intervention program aiming at moderate weight loss or general recommendations for a healthy lifestyle alone. In addition, the study will evaluate the predictive role of cancer-associated and obesity-related biomarkers for the prediction of disease recurrence and survival. This SUCCESS C trial will provide valuable information on the effects of a lifestyle intervention program on the prognosis of early breast cancer patients.

The intervention trials yielded negative results. Nevertheless, in view of the methodological difficulties in this area of research and the overall life situation of women with breast cancer, the authors recommend a health-promoting lifestyle with avoidance of overweight and a low-fat diet rich in fruit, vegetables, and fiber.