Breast Cancer: The Benefits of Exercise 

By Roanne Segal, MD, FRCPC

The five-year, overall survival rate for breast cancer is about 85%; the majority of women will live for a significant length of time after diagnosis.1 Women routinely receive some combination of surgery, chemotherapy, and hormonal and radiation therapy over a prolonged period of time, increasing the incidence of side effects or sequelae.

Side effects generally can be divided into two categories: 1) physical and functional, including fatigue, cardiovascular deconditioning, changes in weight or lean body mass, and muscle weakness, and 2) emotional changes, including depression, anxiety, stress, poor body image, and low self-esteem. Other health problems, including osteoporosis and lymphedema, can have a significant impact on quality of life. This review will summarize the research evaluating exercise as a self-care modality for women at risk for, or living with, breast cancer.

Physical Activity and Risk of Breast Cancer

Over the last decade there has been mounting evidence suggesting an inverse relationship between physical activity and estrogen-dependent cancers. While the exact relationship remains unclear, it generally is accepted that physical activity may affect serum estrogen levels, and several large epidemiological studies have demonstrated an inverse relationship between breast cancer and physical activity.2-5

Thune et al evaluated the influence of physical activity, both at work and during leisure time, on the risk of breast cancer in a cohort of 25,624 pre- and postmenopausal women.4 Data on parity, dietary factors, and body mass index (BMI) were collected and were reassessed after 3-5 years, to estimate the effect of sustained vs. short-term physical activity. During a median follow-up of 13.7 years, 351 incident cases of breast cancer (100 in premenopausal women and 251 in postmenopausal women) were identified.

After adjustments for age, BMI, height, parity, and country of residence, greater leisure-time activity was associated with a reduced risk of breast cancer, (relative risk [RR] 0.63, 95% confidence interval [CI] 0.42-0.95), among women who exercised regularly, as compared with sedentary women (P = 0.04). In regularly exercising women, risk reduction was greater in premenopausal than in postmenopausal women, and greater in women younger than 45 years of age than in older women (RR 0.38; 95% CI 0.19-0.79). In stratified analyses, the risk of breast cancer was lowest in lean women (BMI < 22.8) who exercised at least four hours per week (RR 0.28, 95% CI 0.19-0.70). This risk also was reduced with higher levels of activity at work.4

More recently, Friedenreich et al performed a case-control study of 1,233 breast cancer cases and 1,237 controls between 1995 and 1997 to examine the effect of lifetime physical activity patterns on breast cancer risk.5 Lifetime physical activity was estimated using a questionnaire that assessed occupational, household, and recreational activity. The intensity of physical activity was estimated as light, moderate, or heavy. Definitions were provided for each intensity level, and a specific metabolic equivalent (MET) value then was assigned.

Their results demonstrated important differences between pre- and postmenopausal women. In contrast to the Thune study, no association was found between physical activity and breast cancer risk in pre-menopausal women; reduced risk was noted, but only in postmenopausal women. When comparing those women divided by the highest quartile of metabolic activity (> 161 MET-hrs/wk/yr) vs. those in the lowest quartile (< 104.8 MET-hrs/wk/yr) of lifetime total physical activity, the adjusted odds ratio (OR) was 0.70 (95% CI 0.52-0.94). When type of activity was further evaluated in postmenopausal women, household and occupational activity conferred the largest risk reductions (OR 0.57, 95% CI 0.41-0.79; and OR 0.59, 95% CI 0.44-0.81, respectively).

Although there are no consistent data on when during a woman’s life physical activity might influence breast cancer risk, the data do support a consistent and dose-responsive relationship between the two. Possible physiological mechanisms may include: 1) maintenance of low body fat and moderation of extraglandular estrogen; 2) a reduction in ovarian estrogen production; 3) enhancement of immune function; and 4) an association between exercise and other healthy lifestyle habits.4-6 Why some types of occupational activities appear more favorable than certain recreational activities remains puzzling. Certainly data support recommendations for regular, moderate exercise for at least four hours per week.

Physical Activity in the Setting of Adjuvant Therapy for Breast Cancer

After breast cancer diagnosis, advantages of physical activity include weight control, and physical and psychological benefits. Despite previous concerns that it would be unsafe or unrealistic for women to perform exercise during breast cancer treatment, seven studies support the safety and efficacy of exercise during treatment.7-14 Six studies included a total of 271 women with early-stage breast cancer receiving adjuvant chemotherapy,7-13 while one study evaluated 46 women receiving adjuvant radiation therapy.14

The length of the exercise programs ranged from six weeks to six months, using primarily a moderate intensity, aerobic-based exercise intervention (e.g., walking or a stationary cycle ergometer). Most programs were supervised; two were home-based. All studies followed traditional exercise prescription guidelines. Biosocial outcomes included functional capacity, body composition, fatigue, mood states, and symptoms. Although there were methodological concerns, such as small sample size, relatively short exercise interventions, and limited follow-up, all studies demonstrated significant beneficial effects of exercise during adjuvant therapy, and none reported any adverse events.

Segal et al performed the largest randomized trial to date, designed to evaluate the effects of a structured exercise program on physical functioning and other dimensions of health-related quality of life in women with early-stage breast cancer.13 One hundred twenty-three women were randomized to usual care, a self-directed exercise group, or a supervised exercise group for 26 weeks. Quality-of-life, aerobic capacity, and body weight measures were evaluated. The results supported previous studies: Physical functioning declined in the control group by 4.1 points and increased by 5.7 points and 2.2 points in the self-directed and supervised exercise groups, respectively (P = 0.04). Post-hoc analysis showed a moderately large and clinically important difference between the self-directed and the usual care group (P = 0.01); there was no significant difference between the supervised and control groups. In a secondary analysis of participants stratified by type of adjuvant therapy, only participants not receiving chemotherapy in the supervised exercise group demonstrated improved aerobic capacity by maximal oxygen uptake (+3.5 mL/kg/min; P = 0.01) and reduced body weight (-4.8 kg; P < 0.05) compared with participants in the usual care group.

Rehabilitation for Breast Cancer Patients

There is an increasing body of literature that has examined exercise after breast cancer treatment,15-22 including both correlational and experimental designs. Six correlational studies in which patients were surveyed for several months to many years after completing one or more adjuvant therapies focused on psychosocial outcomes including self-esteem, body image, anxiety, and depression.15-20 Sample sizes ranged from 54 to 500 patients. Four of the six studies found benefits of exercise on the psychosocial outcomes listed above.15,18-20

Six prospective trials were quite small; sample sizes ranged from 12 to 28 patients.21-26 All studies incorporated aerobic exercise into their programs; two studies combined aerobics with weight training.21,23 All studies followed the traditional exercise prescription guidelines in terms of frequency, intensity, and duration of exercise. Outcomes included immune functioning,22-24 lymph-edema,21 and other psychosocial outcomes.25,26 Generally speaking, these studies were less methodologically sound.

Three studies that evaluated immune function were conflicting. Peters found an increase in natural killer cell activity while Nieman23 found no change. In a subsequent study, exercise increased the number of granulocytes with a corresponding decrease in the number of lymphocytes and monocytes.24 Importantly, all patients had completed therapy at least six months previously. Two further studies found increased physical fitness25 and decreased anxiety and depression25,26 in patients who exercised after completing adjuvant therapy.

Exercise and Lymphedema

It has been suggested that exercise—or even lifting heavy objects—increases the risk of lymphedema, but this appears to be a myth. A case series by Harris et al assigned 20 breast cancer survivors, who had undergone surgery with axillary dissection 1-17 years earlier, to a program of upper extremity exercises, including both aerobic and resistance maneuvers. The program was performed three times weekly, for 20-30 minutes at a moderate intensity, for eight months. The primary outcome, change in arm circumference at four locations over time, was unaffected, and there were no differences between arms ipsilateral or contralateral to the side on which surgery was performed.

Conclusion

There is mounting evidence that exercise positively influences several aspects of breast cancer, including prevention, biopsychosocial aspects, and rehabilitation. Promoting exercise is scientifically justified and safe.

Dr. Segal is Associate Professor, Department of Medical Oncology, General Division, and Medical Director, Oncology Rehabilitation Program, Ottawa Regional Cancer Centre, Ottawa, Canada.

References

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