Exercise After Treatment May Improve Survival

M. D. Holmes et al., Journal of the American Medical Association, May 25, 2005

Is this for me?

You might want to read this article to find out how an exercise program can help you after breast cancer treatment.

Background and importance of the study

Research has shown that four hours of exercise a week may lower the risk of developing breast cancer. It's not clear why exercise may have this effect, but one reason might be that exercise can lower the amount of estrogen in your body. Estrogen, a hormone, can promote the growth of some breast cancers, so it makes sense that having less estrogen might mean a lower breast cancer risk.

Other research on exercise and breast cancer has found that exercise also can help boost the immune system, help limit weight gain from chemotherapy, and help ease treatment side effects. Other studies have found that exercise also increases self-esteem and can help to reduce depression, anxiety, and fatigue.

Overweight women have an increased risk of getting breast cancer after menopause. This is most likely because the extra fat cells make various hormones, including extra estrogen. Other research has found that being overweight can increase the risk of breast cancer coming back in women who have had the disease. Regular exercise can reduce the amount of fat in the body and help with weight loss.

Because of these benefits of exercise, researchers have wondered if exercise would help reduce the risk of the cancer coming back in women who have been treated for the disease. In the study reviewed here, researchers from Harvard Medical School and the Dana Farber Cancer Institute looked to see if exercising after breast cancer treatment would increase chances for survival, as well as reduce the risk of the cancer coming back. The study was funded by the National Institutes of Health.

Study design

The researchers used the results of the Nurses' Health Study (NHS) to select a group of women to study. Since 1976 the NHS has been following 121,700 women who are registered nurses. The women were between the ages of 30 and 55 when the study began. They are asked questions about their health through a survey mailed to them every two years.

Out of the 121,700 women, a total of 4,484 women in the NHS were diagnosed with invasive breast cancer. This study looked at 2,987 of these women who were diagnosed with stage I, II. or III invasive breast cancer between 1984 and 1988.

The researchers looked at the amount of exercise that the women did each week starting about two years after diagnosis. Because many women are too tired to exercise while they're recovering from surgery or receiving chemotherapy or radiation, the researchers didn't want to measure exercise levels until after treatment. The women were followed until June 2002.

The women were asked how much time per week they spent on activities such as:

• walking or hiking,
• jogging or running,
• bicycling,
• swimming,
• playing tennis,
• doing calisthenics, aerobics, or aerobic dance,
• using a rowing machine,
• playing squash or racquetball,
• doing yoga, and
• doing other strenuous activities (such as mowing the lawn).

The women also were asked to rate their usual walking pace as casual, normal, brisk, very brisk, or unable to walk.

The researchers gave each activity a MET (metabolic equivalent task) score. The MET score showed how much energy was used for each hour of activity. For example, walking at an average pace has a MET score of 3, and running has a MET score of 12. The researchers calculated total MET hours per week for each woman's activities. For example, if a woman walked at an average pace for 4 hours a week, she had 12 MET hours (4 hours x walking MET score of 3).

The researchers also looked at the following information for each woman:

• the size of the cancer,
• whether cancer was found in the lymph nodes,
• hormone receptor status,
• breast cancer treatments,
• length of time until the cancer came back (recurrence),
• whether breast cancer caused the woman's death,
• menopausal status,
• age at first pregnancy,
• post-menopausal hormone use,
• oral contraceptive use,
• body mass index (BMI), and
• diet.

Results

The women who exercised more than three MET hours each week reduced their relative risk of recurrence (the breast cancer coming back), compared to women who exercised less. Women who exercised more than three MET hours a week also improved survival (reduced the relative risk of dying from breast cancer), compared to women who exercised less.

Relative risk is the number that tells you how much something you do, like exercising, might change your risk, compared to your risk without exercising. The table shows how many MET hours a week were associated with different reductions in women's relative risk of the cancer coming back and improvement in survival:

Of the total group of 2,987 women, 959 women exercised less than three MET hours per week.

Exercising for 9 to almost 20 MET hours a week seemed to offer the most benefits. Keep in mind that the researchers were measuring MET hours of exercise, not just hours. Nine MET hours is about three hours of walking at a moderate pace.

Also keep in mind that the table shows RELATIVE numbers that may seem quite large, not ABSOLUTE ones. Our take-home message (link to the relevant section of the take-home message below) explains the difference.

Exercise and Tumor Pathology

When calculating these reductions in risk, the researchers took into account other factors that can play a role, such as cancer size, lymph node status, and hormone receptor status. They found that women who had hormone-receptor-positive breast cancer appeared to benefit more from exercise than women who had hormone-receptor negative cancer:

• Of women with hormone-receptor-positive breast cancer, those who exercised nine or more MET hours a week (609 women) improved their relative chances of survival by 50% compared to those who exercised less than nine MET hours a week (955 women).
• Of women with hormone-receptor-negative breast cancer, those who exercised nine or more MET hours a week (149 women) improved their relative chances of survival by only 9% compared to women who exercised less than nine MET hours a week (272 women).

Exercise and Weight

Women who weighed more than average benefited more from exercise than women of average weight:

• Of heavier women, those who exercised 24 or more MET hours a week (157 women) improved their relative chance of survival by 48% compared to those who exercised less than 3 MET hours a week (522 women).
• Of normal weight women, those who exercised 24 or more MET hours a week (246 women) improved their relative chance of survival by 39% compared to women who exercised less than 3 MET hours a week (437 women).

Women were considered heavier if they had a body mass index (also known as BMI) of 25 or more.

To calculate your BMI, visit the Centers for Disease Control and Prevention BMI calculator Web page.

Exercise and Stage of Disease

Exercise helped women who had stage I and stage II disease, but seemed to be particularly helpful for women with stage III cancer (only 205 women in this study). Women with stage III cancer who exercised nine or more MET hours a week (76 women) improved their relative chances of survival by 64%, compared to women with stage III disease who exercised less than nine MET hours a week (129 women).

Survival Rates

After five years, the survival rate for women who exercised three or more MET hours a week was 97%, compared to 93% for women who exercised less than three MET hours a week.

After ten years, the survival rate was:

• 86% for women who exercised less than three MET hours a week,
• 92% for women who exercised more than nine MET hours a week, and
• 89% for women who exercised more than three and less than nine MET hours a week.

Conclusions

The researchers concluded that women who exercise more than three MET hours a week after being diagnosed with breast cancer may be able to lower their risk of recurrence and improve their chances of surviving the disease. Women with hormone-receptor-positive breast cancer appear to get the most protective benefits from exercise. The equivalent of walking three to five hours a week at an average pace seemed to have the most benefits. Exercising more than this didn't have greater benefits.

Take-home message

This is a big study that gives us useful information on an important topic: Does exercise after breast cancer help?

Exercise is good for you. The more the better—up to a point. Exercising between three and nine MET hours a week was better than exercising less than three MET hours a week. And women who exercised 9 to 15 MET hours a week did the best. (That's about three to five hours of walking at a moderate pace.) Exercising more than 15 MET hours a week had no extra benefit.

All the women seemed to benefit from exercise, but some benefited more than others:

• Women who had hormone-receptor-positive breast cancer got more benefit from exercise than those who had hormone-receptor-negative cancer.
• Women who weighed more than average got more benefit from exercise more than average-weight women.
• Women with stage III cancer got more benefit from exercising than women who had stage I or stage II cancer. (But since there were only 76 women with stage III cancer in the "more exercise" group, these results may not hold up in a larger study.)

Clearly, exercise is good for you in all kinds of ways: mood, energy, muscles, bones, joints, circulatory system (really gets the heart pumping and the blood vessels working), lungs,—and it's probably important for breast health as well. But you do have to put this into perspective:

• The five-year survival rate for women who exercised three or more MET hours a week was 97%, not much different from the 93% for those who exercised less. And the 10-year survival rate was improved by 86% even for women who exercised less than three MET hours a week, compared to 89% for those who exercised up to nine hours a week and 92% for those who exercised more. So all three levels of exercise offered benefits.
• The relative risk numbers look very big—about a 50% improvement in survival for women who exercised between 9 and 15 MET hours a week. But that big number may only translate into a small change in benefit when you look at ABSOLUTE risk reduction. For example, if your risk of recurrence goes from 5% down to 2.5%, you've had a relative risk reduction of 50% (50% of 5% is 2.5%) but an absolute risk reduction of only 2.5% (5% minus 2.5% = 2.5%).

It can be hard to start exercising. Four hours of exercise a week may sound impossible if you're a lifelong couch potato or if you're sore from surgery, too busy with radiation therapy, or exhausted from chemotherapy. It's hard to force yourself to exercise when you barely have enough energy to get out of bed or off the sofa.

Exercise is an important part of the recipe for good health. Aim for three hours or more a week. If you're not exercising now, try to get moving, and build it up over time. Don't be critical of yourself if you've been inactive. You can start moving today. If you have medical issues such as arthritis or fibromyalgia, ask your doctor or a physical or occupational therapist for safe ways to become more active. If depression is taking away your energy and motivation, seek help from your primary care doctor, a psychiatrist, or a psychologist.

Exercise causes all kinds of chemical and hormonal changes in the body. We have a lot to learn about how and why exercise may be helpful in reducing a woman's risk of breast cancer coming back and improving her chances of survival.