Exercise May Reduce Breast Cancer Risk in African American Women

Pooling data from four large studies of African American women, researchers found that vigorous exercise for 2 hours or more could reduce the risk of estrogen receptor (ER)-positive breast cancer by about 12%. The analysis found no effect for ER-negative breast cancers. The results were published in Breast Cancer Research and Treatment.

Zhihong Gong, PhD, of the department of cancer prevention and control at the Roswell Park Cancer Institute in Buffalo, New York, and colleagues pooled data from 3,856 women diagnosed with breast cancer as well as 16,959 women with no evidence of breast cancer from the African American Breast Cancer Epidemiology and Risk (AMBER) Consortium, which includes four studies: the Black Women’s Health Study, the Multi-Ethnic Cohort Study, the Carolina Breast Cancer Study, and the Women’s Circle of Health Study.

Among the 87.3% of women with breast cancer tumors of known ER status, 64.4% were ER-positive and 35.6% were ER-negative.

Risk factors for diagnosis of breast cancer have been identified, but researchers are also trying to identify behavioral interventions that can mitigate the risk of breast cancer. In this study, the authors sought to examine the ability of exercise to reduce breast cancer risk.

Women of African decent are more likely to be diagnosed with ER-negative breast cancer, which is more aggressive, to be diagnosed at an earlier age, and are more likely to die of their breast cancer.

“Physical activity represents an opportunity to reduce the burden of breast cancer, especially among African American women,” said Gong, in a statement.

Vigorous cardiovascular exercise-running, walking/climbing briskly, cycling, and participation in sports-was associated with a modest but statistically significant decrease in the risk of ER-positive breast cancer (odds ratio, 0.88).

There was a trend toward family history modifying the association of physical exercise and ER-positive cancer development (P = .07).

The authors saw a statistically significant inverse trend across all categories of weekly hours of vigorous physical exercise (P = .007) but no clear dose-dependent relationship with increased hours of exercise.

The study did not find evidence that age, menopausal status, body mass index, or parity affected the decrease in risk through exercise.

“This large study provides further evidence that vigorous physical activity may be associated with a lower risk of breast cancer in African American women. Specifically, 2 or more hours per week of strenuous activity may be sufficient to reduce risk, making physical activity a promising target for intervention to reduce the burden of this most common non–skin cancer among women,” said study coauthor, Christine Ambrosone, PhD, a principal investigator of the AMBER Consortium and senior vice president of population sciences at Roswell Park.

Limitations of the study include self-reported physical activity and pooling of data from several studies with differences in physical activity assessment.