Oct 20, 2010

Healthy Behaviors Lower Overall Breast Cancer Risk

Engaging in ‘breast-healthy’ behaviors – drinking alcohol in moderation, exercising regularly, and watching weight – appear to reduce a woman’s risk for the development of invasive breast cancer after menopause. However, healthy behaviors do not seem to modify risk attributable to a family history of later-onset breast cancer (FHLBC), according to a study published online October 12 in Breast Cancer Research.

An analysis of follow-up data on nearly 86,000 postmenopausal women enrolled in a large observational study indicated that rates of invasive breast cancer among women who reported taking part in all 3 behaviors at baseline (moderate alcohol, regular exercise, weight management) were lower than those of women who said they did not participate in any of the behaviors, report Robert E. Gramling, MD, from the Department of Family Medicine at the University of Rochester, in Rochester, New York, and colleagues from 7 other centers in the United States and Denmark.

However, the benefit of breast-healthy behaviors was seen both in women with an FHLBC (breast cancer in a mother or full sister at 45 years or older) and in women with no affected first-degree relatives, and the degree of benefit did not differ significantly between the groups, the study authors note.

“This study suggests to both public health and office-based clinicians that adherence to breast-healthy behaviors (regular exercise, weight management and alcohol moderation) benefits women with or without a family history of later-onset breast cancer but does not function to reduce family history of later-onset breast cancer-attributable risk,” the study authors write. “Our findings, however, do not address the degree to which behaviors that are discordant from one’s affected relatives might lead to risk reduction.’

Although nearly 15% of postmenopausal women report having 1 or more first-degree relatives with breast cancer, most of the cases appear to involve a combination of genetic, environmental, and behavioral factors vs largely hereditary factors, the investigators write.

“Under such multifactorial inheritance conditions, it is plausible that family history is a mutable risk factor,” they write. “For example, if a woman’s family history arose in part because of a predominance of risk-conferring behaviors among women in her family and she adopts breast cancer-preventive behaviors, she will have ameliorated some of her risk attributed to family history.’

To see whether healthy behaviors could trump family history, the investigators looked at data on 85,644 women from the ages of 50 through 79 years at the time of their enrollment in the Women’s Health Initiative (WHI) Observational Study (1993-1998). Women with a personal history of breast cancer, history of unilateral or bilateral mastectomy, or a family history of early-onset breast cancer in a first-degree relative at enrollment were excluded from the current study.

The primary outcome was invasive breast cancer in the cohort through August 2003 in relationship to lifestyle and risk factors. Breast-healthy lifestyle behaviors were defined as:

  • Alcohol intake of fewer than 7 drinks per week
  • At least 20 minutes of moderate- to vigorous-intensity exercise at least 5 times per week
  • Maintenance of a body mass index from 18.5 to 24.9 kg/m2

The women were followed up for a mean of 5.4 years. A total of 1997 women were diagnosed with an invasive breast cancer during the study.

Among the 9979 with an FHLBC, the rate of invasive cancer was 5.94 per 1000 woman-years for those reporting taking part in all 3 healthy behaviors vs 6.97 per 1000 for those with no healthy habits.

Among the 75,665 women with no reported FHLBC, the rates of invasive breast cancer were 3.51 per 1000 woman-years for the healthy-behavior group vs 4.67 per 1000 for the group that did not participate in healthy behaviors.

The investigators found that family history and lack of healthy behaviors were each significantly associated with increased risk for invasive breast cancer, with respective hazard ratios of 1.50 (95% confidence interval, 1.33 – 1.68) and 1.32 (95% confidence interval, 1.03 – 1.67).

When they looked at the rate of breast cancer that could be attributed to family history in relationship to healthy behaviors, however, they found that there was no dose-dependent relationship. In addition, when they calculated the interaction contrast (IC) to see whether there were additive benefits of healthy habits, they determined that the degree of interaction was not clinically important (IC, 0.00014; 95% confidence interval, -0.00359 to 0.00388).

The study authors acknowledged that the study was limited by the lack of longitudinal assessments, and by the use of FHLBC alone as a proxy marker for multiple potential breast cancer risk factors shared among family members.

Breast Cancer Res. Published online October 12, 2010.

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