Women with dense breast tissue are at an increased risk of breast cancer when compared to women with less dense breast tissue, according to a new study presented at the Second Annual International Conference on Frontiers in Cancer Prevention Research in Phoenix.

In this study of 1,223 women, researchers also found that lower amounts of dense breast tissue were associated with higher physical activity levels in premenopausal women with a BMI (body mass index) less than 30, providing further evidence that exercise may protect against breast cancer.

Participants were enrolled in the Health, Eating, Activity and Lifestyle (HEAL) study, a multicenter study designed to examine the associations between physical activity, diet, weight, hormones, breast density, and other influences on breast cancer prognosis among newly diagnosed breast cancer survivors. Physical activity levels and breast density for this analysis were determined from information and mammographic films from the year prior to diagnosis.

After adjusting for age, ethnicity, education, BMI, study site, number of children, and hormone-replacement use, a statistically significant 17 percent difference in breast tissue density was observed between the least active and most active pre-menopausal women with a BMI less than 30. Researchers found the association between physical activity and breast density only among leaner pre-menopausal women, and not among heavier pre-menopausal women or post-menopausal women in any BMI category.

"We're pleased that we observed an association between physical activity and breast density. We've known that breast density is related to breast cancer risk, and that breast density may change throughout a lifetime. Factors that change breast density may also change breast cancer risk," said Melinda Irwin, Ph.D., MPH, of Yale University and Yale Cancer Center, and lead author of the study.

"This information provides further evidence of the many benefits of regular exercise that could be used to motivate women to be more physically active," she added.

SOURCE:
Second Annual International Conference on Frontiers in Cancer Prevention Research, October 27, 2003, Phoenix, AZ
American Association for Cancer Research (http://www.aacr.org)