Exercise and physical activity did not help protect against in situ breast cancer, or cancer that stays in one part of the body, according to a recently published study.
Though physical activity is good for the body overall, the findings showed that physical activity may provide more benefit in later stages of cancer than in early stages of cancer.
"Get out, get active!"
The study, led by Karen Steindorf, PhD, deputy head and senior scientist in the Unit of Physical Activity and Cancer at the German Cancer Research Center, included more than 280,000 women who were part of the multinational European Prospective Investigation into Cancer and Nutrition.
Within the group, more than 1,000 women had in situ breast cancer. Cancer in situ means the cancer cells haven't yet invaded other tissues of the body. This early form of cancer could lead to an invasive type.
Researchers tracked the women, who were about 51 years of age on average, over an 11-year period. They interviewed women about the hours they spent being physically active, including recreational, household and occupational activity.
At the end of the 11 years, researchers found no links between physical activity and the number of women who had in situ cancer.
Furthermore, physical activity was not tied to the chance of developing in situ cancer. The results did not change across age groups and whether women were pre- or post-menopausal.
Concerning the intensity of activity, the odds that moderately inactive and moderately active participants would develop in situ cancer were about equal.
Specifically, the odds of developing in situ cancer were 0.99 times higher for those who were moderately inactive compared to those who were not moderately inactive. For more active individuals, the odds were 1.07 times higher of developing in situ cancer.
Other studies have shown that physical inactivity is a risk factor for cancer. However, having a higher body mass index (BMI)—a measure of body fat that uses height and weight together—has been linked with invasive cancer. And less physical activity is tied to a higher BMI.
How exercise affects in situ cancer versus invasive cancer could stem from how the cancer started and its origins, according to researchers. They said the different cancers are separate diseases.
"In conclusion, this large prospective study conducted in a heterogeneous population of European women provides no evidence for an association between physical activity and risk of in situ breast cancer," researchers wrote in their report.
Based on the findings, researchers said that any beneficial effects physical activity might have on cancer could be more prevalent later on in the cancer process.
The authors noted that the level of physical activity reported at the start of the study might not represent long-term activity. The frequency and duration of the activity was also not included.
The study was published in the December 2012 issue of Cancer Epidemiology, Biomarkers & Prevention. No conflicts of interest were reported.
Funding for the study was provided by a number of national and international institutions, including the European Commission and the International Agency for Research on Cancer.