October 26, 2011 (Boston, Massachusetts) — Data supporting the association between physical activity and a reduced risk for breast cancer are increasing. Adding to these data are the results of a large European study, presented here at the Tenth Annual American Association for Cancer Research International Conference on Frontiers in Cancer Prevention Research.
When the researchers compared the highest and lowest quartiles of physical activity, the risk for invasive tumors was inversely associated with high levels of total physical activity (hazard ratio [HR], 0.85; P trend < .001), especially recreational activity (HR, 0.88; P < .001).
However, no association was seen between in situ carcinoma and any of the physical activity variables.
The researchers also looked at the effect of physical activity on breast cancer risk by receptor status, and note that this is the largest prospective study to do so. Previous studies investigating this issue have yielded inconsistent results, explained study author Karen Steindorf, PhD, from the German Cancer Research Center in Heidelberg.
The researchers found a significant protection of physical activity only for the estrogen-receptor (ER)-positive and progesterone-receptor (PR)-positive tumor types, said Dr. Steindorf. "These findings strengthen the hypothesis that lowering breast cancer risk with physical activity is at least partly related to hormonal pathways."
The association between breast cancer risk and physical activity also differed by menopausal status. "There were significant risk reductions in postmenopausal breast cancer," she said, adding that the risk reductions were a little lower in premenopausal women.
Among postmenopausal women, the risk reduction was significant for both total physical activity (HR, 0.81; P = .002) and recreational activity (HR, 0.89, P = .005). These results were slightly less robust for premenopausal breast cancer for total physical activity (HR, 0.87; P = .082) and for recreational activity (HR, 0.84; P = .032).
"I would say that this adds to the evidence of what we have already seen in other research — that physical activity may reduce the risk of breast cancer," said Karen T. Liby, PhD, research assistant professor of medicine at Dartmouth Medical School, Hanover, New Hampshire, who was not involved in the study. "But it seems to be effective only in receptor-positive cancers."
Exercise Linked to Lower Risk
As previously reported by Medscape Medical News, postmenopausal women who maintain a regular moderate to vigorous exercise program can reduce their risk for breast cancer by 20% to 40%. In addition, research has shown that physical activity can reduce the risk in premenopausal women; among the most active women, risk reduction can be as high as 23%.
Other data have shown that obesity and lack of physical activity can increase the risk for triple-negative breast cancer.
Protective Effects Confirmed
Dr. Steindorf and colleagues used data from the European Prospective Investigation Into Cancer and Nutrition (EPIC), a large study designed to investigate the relation between diet, nutritional status, and lifestyle and environmental factors and the incidence of cancer and other chronic diseases. The trial has recruited 520,000 people from 10 European countries.
Detailed information on recreational household physical activity, occupational physical activity, and other variables was assessed in a baseline examination conducted between 1992 and 2000. The cohort in this trial involved 283,680 women; within this group, at a median follow-up of 11.7 years, there were 9947 incident breast cancer cases, including 1060 cases of in situ carcinoma. Of the 8887 invasive breast cancer cases, it was possible to assess the ER status of the tumor in 6007 cases (67.6%), the PR status in 4814 cases (54.2%), and the combined status in 4798 cases (53.9%).
When analyzed by hormone-receptor status, stronger effects of total physical activity were seen for ER-positive/PR-positive breast tumors than for other combinations (P = .043 for heterogeneity). A more detailed analysis revealed that it was primarily the PR status (P = .006 for heterogeneity), not the ER status (P = 0.235 for heterogeneity), that dominated this result.
The protective effect of physical activity on breast cancer risk is confirmed with these results, note the researchers. "The results of this largest prospective study on physical activity and different hormone-receptor status indicate that physical activity primarily reduces the risk for PR-positive and ER-positive/PR-positive tumors," they conclude.
Tenth Annual American Association for Cancer Research (AACR) International Conference on Frontiers in Cancer Prevention Research. Presented October 24, 2011.
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