A "favorable" lifestyle was associated with a reduced risk of breast cancer even among women at high genetic risk for the disease in a study of more than 90,000 women, researchers reported.
The findings suggest that, regardless of genetic risk, women may be able to reduce their risk of developing breast cancer by getting adequate levels of exercise; maintaining a healthy weight; and limiting or eliminating use of alcohol, oral contraceptives, and hormone replacement therapy.
With almost a quarter of breast cancers thought to be preventable in the United Kingdom, "it is important to understand the contribution of modifiable risk factors ... and how they affect or add to the inherited genetic factors," the researchers wrote.
To that end, the team reviewed 91,217 white, postmenopausal women in the United Kingdom Biobank, an ongoing longitudinal study of the contribution of genetic, environmental, and lifestyle risk factors in disease. There were 2,728 women who developed breast cancer at a median follow-up of 10 years.
The investigators used a polygenic risk score to categorize subjects as low, intermediate, or high genetic risk. The score was constructed using 305 single-nucleotide variants.
Within each risk group, the researchers divided women by the presence or absence of five lifestyle factors previously associated with a lower risk of breast cancer: healthy weight, regular exercise, no use of hormone replacement therapy beyond 5 years, no oral contraceptive use, and alcohol intake no more than twice a week.
Women with four or more of these factors were deemed to have a favorable lifestyle. Women with two or three factors had an intermediate lifestyle, and women with fewer factors had an unfavorable lifestyle.
The data showed an association between breast cancer and a body mass index of 25 or higher (relative risk, 1.14), no regular physical activity (RR, 1.12), alcohol intake at least three times per week (RR, 1.11), and use of hormone replacement therapy for 5 or more years (RR, 1.23). History of oral contraceptive use was not associated with breast cancer risk (RR, 1.02), but this factor remained a part of the lifestyle classification.
In the intermediate genetic risk group, intermediate (HR, 1.37; 95% CI, 1.12-1.68) and unfavorable lifestyles (HR 1.94; 95% CI, 1.46-2.58) were again associated with higher breast cancer risk, compared with a favorable lifestyle .
Even in the high genetic risk group, intermediate (HR, 1.13; 95% CI, 0.98-1.31) and unfavorable lifestyles (HR, 1.39; 95% CI, 1.11-1.74) were associated with increased breast cancer risk. Results were adjusted for both age and family history.
In the end, "a healthier lifestyle ... appeared to be associated with a reduced level of risk for [breast cancer], even if the women were at higher genetic risk," the researchers wrote. "Our findings suggest that women may be able to alter or reduce their risk of developing [breast cancer] by following healthier lifestyles," regardless of genetic predisposition.
It's "surprising that these lifestyle changes lowered the risk of breast cancer," said Charles Shapiro, MD, of the Icahn School of Medicine at Mount Sinai in New York, who was not involved in this study.
The study "requires replication," he said. "On the other hand, these lifestyle changes promote overall health and certainly are associated with decreased risks of cardiovascular disease, the number one killer of women."
"Patients always want to know what they can do above and beyond screening mammograms to reduce their risk of developing breast cancer," said William Gradishar, MD, of Northwestern University in Chicago, who was not involved in the study.
"These data should empower patients that they can impact on their overall health and reduce the risk of developing breast cancer," he said.
Among the study's limitations, it's unclear how the findings apply to nonwhite, nonpostmenopausal women, and the analysis did not differentiate between breast cancer subtypes.
In addition, although oral contraceptives have been linked to breast cancer in the past, there was no association in this study. Possible explanations could be that the investigators did not take into account duration of use, age of last use, and type of oral contraceptive used, they noted.
This research was funded by the National Institute for Health Research Manchester Biomedical Research Centre, the Alan Turing Institute, and a Cancer Research UK Integrated Cancer Epidemiology Programme grant. The investigators, Dr. Gradishar, and Dr. Shapiro have no relevant disclosures.
SOURCE: Al Ajmi K et al. JAMA Netw Open. 2020;3(4):e203760.
This article originally appeared on MDedge.com.
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Cite this: Lifestyle Choices May Reduce Breast Cancer Risk Regardless of Genetics - Medscape - Jul 07, 2020.