Can Exercise Help Prevent Breast Cancer?: A Dana-Farber Q&A
Chances are you either personally know somebody who has been diagnosed with breast cancer or know somebody who knows somebody who has been affected by the disease. Last year alone, there were more than 2.8 million women in the U.S. with a history of breast cancer.
The good news is that an increasing number of women who are newly-diagnosed with breast cancer are completing treatment and can be considered “breast cancer survivors,” thanks to innovations in cancer treatments, as well as improved screening methods and increased awareness.
Yet breast cancer deaths remain higher among women in the U.S. than mortality rates for any other cancer, other than lung cancer. Although death rates from breast cancer have declined over the past few decades, nearly 40,000 U.S. women die of breast cancer every year.
Even though the number of new cases of breast cancer in the U.S. increased from 105.1 (per 100,000) to 126.5 between the years 1975 and 2010, the number of deaths decreased from 31.4 to 21.9 (per 100,000).
In their efforts to decrease breast cancer mortality rates, scientists are focusing largely on developing ways to prevent cancer recurrence instead of waiting to treat a patient if or when the cancer does recur. Common treatments include localized radiation therapy and drug therapy, as well as more individualized approaches such as post-operative hormonal treatments and immunotherapy.
At the same time, many recent studies have explored how people who have been diagnosed with breast cancer may benefit from making lifestyle changes—particularly exercise. Resistance and impact training, for example, has been shown to help older women build muscle strength and reduce risk of bone loss—a finding particularly noteworthy because the majority of U.S. women with breast cancer are over the age of 50. Another study, published in the International Journal of Cancer, found that exceeding current exercise recommendations and adding running to an exercise program may increase chances of survival, compared to simply meeting the minimum exercise recommendations. A third study at the Yale Cancer Center concluded that lifestyle changes—such as healthy eating and regular exercise—can lower biomarkers associated with breast cancer recurrence and mortality.
Although these studies collectively point to the overall benefits of exercise, it is important to distinguish between studies that examine the relationship between exercise and disease prevention and studies that examine the effectiveness of exercise as a complementary or alternative treatment. To find out more about the benefits of exercise in terms of breast cancer prevention versus breast cancer treatment, HealthCentral interviewed Dr. Jennifer Ligibel, a senior physician at the Susan F. Smith Center for Women’s Cancers at Dana-Farber Cancer Institute who specializes in the effects of exercise on breast cancer survivors.
[An edited transcript of the interview follows.]
What does scientific evidence conclude about the link between physical activity and breast cancer risk in terms of prevention?
The majority of observational studies on this topic demonstrate that people who are more physically active are at lower risk of developing breast cancer—by about 20 to 30 percent when you look at the people who are most active versus least active. Studies that looked at all different kinds of activity at all different time points suggest that being active definitely does lower your risk of breast cancer—not by 100 percent, but by a significant amount.
Are most cases of breast cancer preventable?
I absolutely do not feel that we could possibly say that. I think that people think that there may be cases of breast cancer that are linked to lifestyle factors, but we don’t have definitive evidence that shows that changing a lifestyle factor could prevent breast cancer. We hope that’s true, but we don’t know that that is true at this point.
I just want to clarify: There are no studies at all that show that changing a behavior changes risk. There are studies that look at different patterns and how they are related to somebody’s risk, but there are not studies that show that changing behaviors show a change in risk. We just know that people who are more active appear to be at lower risk. But we don’t know that if you take somebody and you change their exercise pattern that that person is going to lower their risk. It’s a little bit of a hard topic, and this is why observational research is always a little bit difficult to describe. We can talk about what happens in patterns of people, but we can’t tell you what happens for an individual if they make a change.
Can exercise reduce risk of breast cancer in women who are already at high risk due to family history or genetic factors?
There are some data that suggests that people who are BRCA carriers who exercise may also have lower cancer risk—a later development of breast cancer compared to women who don’t—but I think that a lot of times people who have those types of risk—that is such a driving factor—that some of the lifestyle factors like exercise and weight may not be quite as powerful in that group of women.
What is the takeaway for people regarding the link between breast cancer and exercise?
What I would say is that we know that women who exercise regularly are at lower risk of breast cancer. What we can’t tell is if she starts exercising today, whether or how much that will decrease her personal risk. We know that in the general population, people who exercise seem to be at lower risk; whether that’s specifically because of exercise or because of other things that they’re doing as well is what we can’t definitively conclude yet.
Based on current findings, what are future studies going to focus on in terms of breast cancer prevention?
In terms of prevention, there’s a lot that we’re trying to figure out—what happens when someone exercises that influences cancer. There are studies that look at what happens to people’s insular levels, their metabolism, what happens to their inflammation—so there are studies like that going on. There are some studies going on that are trying to figure out what are the most effective ways of making beneficial improvements to those things—like what kind of exercises are beneficial and what patients get the most benefit from it.
Right now there aren’t any planned big trials to test really whether exercise will reduce a woman’s risk of developing breast cancer. Those studies require, you know, 10,000 patients, and they take a very long time. And that unfortunately is not something that is viewed as being very possible in the current state of medical research, but I hope one day we are able to do a study like that.
What about the benefits of exercise for breast cancer survivors—what does evidence conclude about exercise and breast cancer recurrence and death?
We know from a number of studies that if you take somebody that’s not exercising and has been diagnosed with cancer, and then they start to exercise, that that will have a number of very favorable benefits from a physical and emotional standpoint for that person. Exercise reduces fatigue or tiredness—which is a chronic problem for many people who have cancer or have gone through cancer therapy—it gives people more endurance, it helps them to be stronger and regain their strength more quickly after treatment, they have better quality of life, less anxiety and depression, and they have fewer side effects of therapy in many studies.
Additionally, studies show that people who exercise regularly seem to have lower risk of recurrence and dying from cancer. There has never been a cause-and-effect study done, but many studies suggest that women who do exercise seem to have about a 30 to 50 percent lower risk of dying from breast cancer as well as having their cancer come back. We can’t say that if somebody starts to exercise, that that’s going to reduce their risk of cancer by 50 percent. But study after study suggests that women who exercise do better from their cancer, so it’s really promising evidence.
What do these studies mean for people who want to become more physically active?
The current guidelines recommend 150 minutes of moderate intensity exercise a week, like walking, combined with 2-3 strength training sessions, as a goal for cancer survivors. What I tell my patients, especially if they’re not doing anything at all, is that doing a little bit of exercise is better than none, and we really recommend that people start out slowly, that they set very realistic goals, and that they increase their exercise by a small amount each week to really build up their endurance so that you don’t put yourself at risk of injury. And we usually recommend that everybody talk to their doctor before they start exercising just to make sure that there’s not anything special that they should keep in mind.
What should women who have had surgery be aware of? For example, could women who have had a mastectomy/lymph node removal end up with lymphedema if they exercise too intensely?
It used to be that we told women who have had surgery not to exercise at all with that arm. But we’ve come to recognize that that really is not the right strategy, and that if you don’t ever use your arm ever your muscles really get weak, and your range of motion gets limited. Many studies show that weight training does not necessarily increase the risk of lymphedema; in fact, studies would get to the point where women lifted fairly heavy weights with that arm—there wasn’t like an upper limit of how much you should lift—but it was really important to progress very slowly and to not make big jumps and start too fast too soon. That was why the recommendation was that people should at least consider meeting with a trainer who has a certification in oncology or physical therapist or somebody that could provide more of a step-wise program so that you didn’t do too much so soon. So aerobic exercise is fine, even with more intensive exercise like running, there’s not concern regarding that. We’re more concerned when people want to do weight lifting with their upper body if they’ve had lymph node surgery—they should consider meeting with an exercise specialist just to make sure that they don’t progress too quickly.
Or sometimes if women have gotten chemotherapy that causes them to have neuropathy or diminished sensation in their feet, that could be another situation where they might want to have a little bit more consideration. If they’re doing things like walking, it could be a little bit more challenging, so they may want to explore cycling or swimming instead.
How much of a factor do lifestyle changes play in long-term health?
For many breast cancer patients with early stage breast cancer, their risks of breast cancer recurrence are actually a lot lower than their risk of developing heart disease or other medical problems. But sometimes with the therapies that women receive, some women will gain weight in chemotherapy or they’ll become less active, and those types of things may ultimately have a bigger impact on their risk of developing other medical problems that are more significant than their risk of breast cancer recurrence. So I think it varies for the individual patient and the stage of disease, but I do think that lifestyle is pretty important for most people after breast cancer diagnosis.
The graph below illustrates the stages of breast cancer and corresponding five-year relative survival rate, which compares the observed survival with what would be expected for people without cancer. Hover over graphic to read more about each stage of cancer.
People with stage 0 (non-invasive) cancer have about a 100 percent chance of survival over five years, compared to people with stage IV cancer, who have a relative five-year survival rate of 22 percent.
People who exercise typically experience less joint pain from aromatase inhibitors, they have better body image, they have less anxiety and depression, and they have better overall quality of life. There are definitely a lot of very real day-to-day benefits of exercise for survivors that have been now shown in many, many studies looking at all different kinds of exercise. From what we’ve seen so far, it doesn’t seem to really matter if somebody’s walking or riding a bike or doing an aerobic form of yoga—these things seem to all have benefits for people.
What are some good resources for people looking to change their diet/exercise routine after breast cancer?
The American Cancer Society has some very nice lifestyle recommendations for cancer survivors that I think are always a good guide. In addition to the recommendations for exercise, they also recommend that people try to keep their weight in a healthy range, and if they’re overweight or obese, that they try modest weight loss. And they recommend a healthy diet—fruits and vegetables, limitations of processed foods and sweets, encouraging whole grains over simple sugars and limiting alcohol.
And the LIVESTRONG at the YMCA is a community-based exercise program available in YMCAs across the country. It is a 12-week program group for cancer survivors to really get people moving again after cancer diagnosis. That’s one of the few national programs that exist that help people get moving. The ASCO (American Society of Clinical Oncology) just released some new materials for lifestyle change in cancer survivors—it’s available on cancer.net. It’s materials about weight management and obesity and provides a lot of resources both nationally and instructions about how to find local resources to help people make healthy lifestyle changes, improvements in diet and weight loss, and increase activity after cancer diagnosis.
What message do you want to leave people with?
At the end of the day, we really want to encourage people. Going through cancer is a very scary experience. It’s also a time when I think people really examine their lives and can make very powerful changes to improve their lifestyles and lead healthier lives. One of the things I’ve been involved in in the ASCO (American Society of Clinical Oncology) initiative is that we really want to help health care providers give their patients information to really help them use a cancer diagnosis to make their lives healthier overall. And that’s something that we really want to help support people in doing. Sometimes as a physician that takes care of cancer patients, we’re very focused on the medicines they need and the different medical therapies, and I think I’d also encourage people to think about how to help their patients make healthier lifestyle changes to help them strengthen their bodies and minds in the years after their cancer diagnosis and come away from it as a healthier person overall.
Read more about the work at Dana-Farber Cancer Institute, who, since its founding in 1947, has been committed to providing adults and children with cancer with the best treatment available today while developing tomorrow’s cures through cutting-edge research.
Ligibel, Jennifer, M.D. Telephone interview. 4 June 2014.