When it comes to lowering breast cancer risk for older women, the research is clear that both physical activity and staying a healthy weight play an important role. Evidence also suggests — but is not as strong — that these factors may improve survival after diagnosis of breast cancer.
Now an animal study attempting to tease apart the impact of exercise and weight stability on breast tumors finds that both being active and consuming slightly fewer calories to avoid weight gain produced healthy changes in immune cells and the tumor environment.
The paper is the first to show that the combination of activity and keeping a stable weight — at least in mice — can reduce metastasis. This needs more support and human evidence before its findings can be applied to women.
The study was partially funded by AICR. It was published in Cancer Prevention Research.
AICR/WCRF’s recent analyses of the global research show that avoiding weight gain as an adult and being active can independently lower post-menopausal breast cancer risk.
“This study is important because we looked at primary tumor growth but we also looked at metastases, which is hard to do in animal models,” said AICR grantee Connie J. Rogers, PhD, Associate Professor at The Pennsylvania State University and lead author of the study.
“Exercise has been such a black box and it affects so many things.… We wanted to look at the biological processes affected by both activity and the prevention of weight gain.”
This animal study adds to the research working to understand how exercise affects both prevention and survival. It follows the recent publication of a small human study — also funded by AICR – that found some of the first evidence in humans that exercise can directly impact tumor gene expression, especially in pathways involved in inflammation and immune regulation.
“These studies really show the importance of supporting the full spectrum of research from the laboratory to the clinic,” said Nigel Brockton, PhD, AICR’s Vice President of Research. “The human studies are necessary to demonstrate the relevance and impact. The laboratory research helps us dig into the details of how it all works so that we can design the most effective interventions to reduce risk and improve survival/outcomes.”
Mice, active and eating less
For the study, mice were randomized into active and sedentary groups. Some in each group were fed as much as they wanted while others were given a 10 percent calorie cut to their standard diet. This was to prevent weight gain, mirroring the slight but creeping weight gain that happens to the average American over time.
After several months, it was the mice that were both active and on the restricted diet that showed reduced tumor growth and increased survival compared to the other groups. This combination group also showed less metastasis to both the lung and bone.
This study modeled the relatively rare triple-negative breast cancer. This type occurs in about 10 to 20 percent of breast cancers and, is more challenging to treat and has a poorer prognosis.
When Rogers and her colleagues conducted further tests, they found changes in genes and cells that affect tumor growth among the active, calorie-restricted group. The biological changes related to immune cells and its surroundings. The tumor’s surroundings, called its microenvironment, can play a major part in tumor growth.
“In our genetic analysis, it looks like there is some effect of energy restriction alone and some with activity but it really looks like it’s the combination of both that allows a different gene expression profile,” said Rogers. “This is telling us that we may be able to change how a tumor behaves with a lifestyle intervention and, as we learn more, maybe in combination with therapy.”
This is similar to the conclusion of the recent study conducted among a small group of women diagnosed with breast cancer, which suggested that exercise may have a direct effect on breast cancer.
What is clear now on lowering risk
Along with regular activity and preventing weight gain, staying a healthy weight and avoiding alcohol are other key steps to lower breast cancer risk. Staying a healthy weight is one of the most important ways to reduce risk of both post-menopausal breast and many other common cancers, including colorectal and ovarian, AICR research shows.
For breast cancer, even small amounts of regular alcohol intake increase risk some amount. If you do drink alcohol, AICR recommends women have no more than one drink a day.
You can read more about the findings on how to lower breast cancer risk here.
Along with AICR, the study was supported by the Broadhurst Career Development Funds and National Institutes of Health.