Of the modifiable lifestyle factors, it is primarily hormone replacement therapy and a lack of physical activity which increase a woman's risk of developing breast cancer. Alcohol consumption and overweight were found to have less influence on breast cancer risk. Thus, 19.4 percent of invasive postmenopausal breast cancer are attributed to hormone replacement therapy; 12.8 percent to a lack of physical activity. Both factors together are responsible for 29.8 percent of breast cancer cases. When the investigators took a separate look at the group of patients whose tumors have receptors for sex hormones (hormone receptor-positive breast tumors), they determined an even higher value of 37.9 percent. The study leaders emphasize that these results reflect the situation in Germany with our typical lifestyle and may differ in countries with other lifestyles.

Non-modifiable factors such as family history or age at first and last menstrual period account for 37.2 percent in total of all malignant postmenopausal breast cancers. "That means that two factors which each woman has in her own hands are responsible for a similar number of postmenopausal breast cancer cases as the non-modifiable factors," Karen Steindorf says. "If behavioral changes in these two areas could be brought about, almost 30 percent of breast cancers after menopause could be prevented." Therefore, the DKFZ researchers recommend women to take more exercise and to refrain from hormone replacement therapy, unless it is absolutely necessary.

Source: Helmholtz Association of German Research Centres