Nearly a quarter-million women were diagnosed with invasive breast cancer in 2016 (1). Further, an estimated 40,000 women lost their lives to breast cancer, making it the second deadliest type of cancer (1). Over the past decade, incidence rates of breast cancer have largely remained stable, although mortality rates have slightly declined (1). Despite these positive changes, more work is necessary to better understand how to prevent and treat breast cancer to improve overall population health.
Lifestyle behaviors have long been identified as risk factors for both the development of, and negative outcomes from, cancer. For example, obesity (body mass index [BMI] of 30 kg·m2 or higher) is associated with a 20% to 40% increased risk of breast cancer in postmenopausal women (22). Further, in patients diagnosed with breast cancer, obesity is associated with a 33% increased risk of recurrence and all-cause mortality in a recent meta-analysis of 43 studies (26). Combined obesity and physical inactivity account for an estimated 25% to 33% of all breast cancer (18).
Factors known to be protective for breast cancer include maintaining a healthy weight and engaging in regular moderate or vigorous exercise. Unfortunately, exercise remains an underused preventive strategy, with objective studies observing fewer than 10% of US adults engaging in the recommended amount of physical activity (9,34). Patients who are concerned about their cancer risk, as well as those who are cancer survivors, represent an important target population given the additional impact exercise can have in improving their health. Further, patients affected by cancer may be particularly motivated to exercise if made aware of these potential health benefits. Clinicians can play a critical role in motivating patients to make behavioral changes for healthier lifestyles (25). Unfortunately, the rate of clinician counseling for exercise has declined in the face of the obesity epidemic (15).
Primary care clinicians serve on the frontline of patient care, and therefore, can benefit from the latest findings in the field of breast cancer prevention and treatment. The purpose of this review is to highlight recent articles that examine the impact of exercise on breast cancer prevention and treatment. Understanding the current literature in this area can help clinicians understand how best to interpret study results for patients and encourage exercise counseling. Successfully engaging more women in exercise can decrease breast cancer morbidity and mortality and ultimately improve the health of the US population.
Role of Exercise in Prevention of Breast Cancer
Although physical activity is well known to decrease risk of heart disease and all-cause mortality (11,21), the association with cancer risk has only recently been better understood. Given increasing scientific literature in this area, the World Cancer Research Fund, in partnership with the American Institute for Cancer Research, updated their 1997 report to include physical activity in 2007 — “Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective”(36). The second recommendation of this report is to “be physically active as part of everyday life,” given the increased awareness that physical activity is protective against cancers as well as weight gain, overweight, and obesity. With particular regard to postmenopausal breast cancer, this literature review identified sufficient evidence from prospective studies that higher levels of physical activity, with a dose-response relationship, lowered the risk (36). Further, the American Cancer Society also recommends engaging in a physically active lifestyle, in line with the 2008 Physical Activity Guidelines for Americans (16). Physical activity impacts cancer risk through various mechanisms, including metabolic (i.e., caloric balance), hormonal, and immune effects (19).
A recent study by Moore and colleagues (20) pooled data from 12 prospective US and European cohorts with self-reported physical activity measures to determine the association of physical activity with incidence of 26 types of cancer. A total of 1.44 million participants with 186,932 cancers were included in the analysis. Leisure-time physical activity was determined for each individual and examined for contrast in those individuals with either high (at the 90th percentile) or low (at the 10th percentile) activity levels. High versus low levels of physical activity was associated with lower risk of 13 cancers, including breast cancer (hazard ratio [HR], 0.9; 95% confidence interval [CI], 0.87 to 0.93). Further, this study extended current understanding of high levels of physical activity and its inverse association in patients with estrogen receptor-negative breast cancer (20). The study authors concluded that health care professions should emphasize with patients the benefits of being physically active in cancer prevention, even in the setting of high BMI or smoking history.
Understanding how to help women be more physically active to reduce cancer risk remains a challenge. Technology-based interventions have been explored as an avenue for women at risk for breast cancer. Hartman and colleagues (10) tested the efficacy of a 3-month social cognitive theory grounded Internet-based physical activity targeting sedentary women with a family history of breast cancer. Given that this intervention was delivered entirely through technology, it overcomes several barriers of program dissemination, including being time intensive and having expensive delivery channels. The intervention was modified from a print-based physical activity intervention and included an Internet-based program with brief telephone counseling for personalized goal setting and discussion. Participants were encouraged to work up to 45 to 60 min of moderate intensity physical activity most days of the week. Participants (n = 56) had a mean age of 42.6 yr, predominantly white (93%) with a mean BMI of 27.3 kg·m2. At 3 months, intervention participants had significantly greater increases in minutes of moderate to vigorous intensity physical activity (approximately 14 to 213 min·wk−1) as compared with the participants in the control arm (30 to 129 min·wk−1). Significant differences were maintained at 5 months, 2 months after the intervention ended. Study authors suggested that the maintained benefit after the conclusion of the intervention was a result of improvement in self-efficacy (10). Understanding effective interventions utilizing Internet-based programming has tremendous potential for future dissemination.
Role of Exercise After a Diagnosis of Breast Cancer
Numerous recent studies have investigated the role of exercise after a diagnosis of breast cancer, demonstrating improvement for perioperative outcomes, treatment side effects, quality of life, and overall survival.
Given that postoperative recovery is important for both patients and society through health care expenditures, understanding how exercise can be of benefit is important. Preoperative exercise may be useful for perioperative outcomes among women with breast cancer. A study of 220 patients undergoing breast cancer surgery found that women who were more active had an 85% increased chance of feeling physically recovered 3 wk postoperatively (relative risk [RR], 1.85; 95% CI, 1.2 to 2.85) (24). However, no difference was demonstrated at 6 wk, due to the fact that most women felt physically recovered. Further, no difference was found in length of sick leave or self-assessed mental recovery between patients who were inactive versus active (24).
A Cochrane Review was conducted in 2016 to assess the effect of aerobic or resistance exercise interventions during adjuvant treatment for breast cancer on treatment-related side effects (6). This review was an update of the original Cochrane review published in 2006 and included randomized controlled trials of exercise interventions on outcomes including physical deterioration, fatigue, quality of life, depression, and cognitive dysfunction. A total of 32 studies were included with 2626 randomized women. The review concluded that physical exercise during adjuvant treatment for breast cancer probably improves physical fitness (standardized mean difference [SMD], 0.42; 95% CI, 0.25 to 0.59, moderate-quality evidence) and slightly reduces fatigue (SMD, −0.28; 95% CI, −0.41 to −0.16). Unfortunately, exercise led to little or no improvement in health-related and cancer-specific quality of life and depression. The study authors concluded that exercise can be regarded as a supportive self-care intervention with probable improvement on fatigue and physical fitness. However, at least nine current studies were ongoing at the time of the review to help answer the questions of if, and how much, exercise helps with both these and other treatment side effects.
A second Cochrane Review published in 2017 focused on the role of yoga in improving health-related quality of life, mental health, and cancer-related symptoms in women diagnosed with breast cancer. Although also a form of exercise, yoga additionally incorporates meditation and breathing exercises as well as spiritual practice and is a complementary therapy often recommended for patient with cancer. This review included 24 randomized controlled trials with a total of 2166 participants. Moderate-quality evidence supported yoga as having a short-term (≤12 wk effect improving health-related quality of life (SMD, 0.22; 95% CI, 0.04 to 0.4), reduced fatigued (−0.48; 95%CI, −0.75 to −0.20), and reduced sleep disturbances (SMD, −0.25; 95% CI −0.4 to −0.09). However, the review did not find that yoga reduced depression or anxiety or improved health-related quality of life and fatigue in the medium term (30 to 48 months).
Another treatment-related side effect of breast cancer that exercise may address is lymphedema. Breast cancer-related lymphedema is the accumulation of fluid in the interstitial tissues in the arm, shoulder, neck, or torso attributed to the damage of lymph nodes during breast cancer treatments involving radiation and axillary node dissection (23). Nelson (23) conducted a systematic review of the literature of randomized controlled trials investigating the effect of resistance exercise in those with, or at risk for, breast cancer-related lymphedema. A total of six good quality randomized controlled trials were identified, including 805 breast cancer survivors. Strong evidence was identified that breast cancer survivors can perform resistance training exercise to produce significant gains in strength without risk of incidence or exacerbation of lymphedema. Practical applications suggested by this review included that progressive resistance exercise training can be safely performed two to three times a week on nonconsecutive days. However, medical approval was recommended before initiation of a resistance exercise training program.
In addition to impacting treatment side effects, evidence suggests that physical activity decreases breast cancer recurrence and overall mortality. A systematic review of 16 prospective studies of breast cancer survivors found a summary relative risk of total and breast cancer mortality of 0.77 (95% CI, 0.69 to 0.88) and 0.77 (95% CI, 0.66 to 0.9), respectively, for cancer survivors with the highest versus lowest levels of prediagnosis physical activity (29). For postdiagnosis physical activity, the summary RR of total and breast cancer mortality were 0.52 (95% CI, 0.42 to 0.64) and 0.72 (95% CI, 0.60 to 0.85), respectively. Further, survival was incrementally tied to amount of exercise: each 10 metabolic equivalent task-hour per week increase in postdiagnosis activity was associated with 24% (95% CI, 11% to 36%) decreased total mortality risk among breast cancer survivors. Schmid and Leitzmann’s review also demonstrated that benefit for survivors who were sedentary before diagnosis: survivors who increased their physical activity by any level from prediagnosis to postdiagnosis showed decreased total mortality risk (RR, 0.61; 95% CI, 0.46 to 0.80) compared with those who did not change their physical activity level (29).
Borch and colleagues (2) further added to this evidence in their study of 1327 women with breast cancer from the population-based Norwegian Women and Cancer study. Although they did not find an association of prediagnostic physical activity levels with all-cause or breast cancer-specific mortality, postdiagnostic physical activity level was associated with a significant decrease. Specifically, all-cause mortality (HR, 1.76; 95% CI, 1.21 to 2.56) and breast cancer-specific mortality (HR, 2.05; 95% CI, 1.35 to 3.10) increased among women who were less active after diagnosis. These findings highlight the importance of integrating physical activity postdiagnosis, regardless of prediagnosis activity level. Clinicians may find that sharing this evidence with patients who are currently sedentary may be particularly motivating.
In addition to the side effects outlined above, treatment for breast cancer also is associated with increased body fat and decreased lean body mass, unfortunate changes which increase the risk of obesity and resultant increased risk of cancer recurrence and mortality (5). Zhu and colleagues (38) conducted a meta-analysis of randomized controlled trials investigating the effects of exercise intervention in breast cancer survivors. Thirty-three trials met inclusion criteria and were included with a total of 2659 patients. In addition to results demonstrated in the Cochrane Review (quality of life, self-esteem, and depression and anxiety symptoms), exercise was found to increase muscular strength and improve body composition, including reducing BMI and fat mass and increasing lean mass (38).
Aromatase inhibitors, guideline-concordant treatment for postmenopausal women with hormone receptor-positive breast cancer, are associated with several negative side effects. Up to 50% of patients treated with aromatase inhibitors have associated arthralgias, resulting in poor medication adherence and increased mortality. Breast cancer treatment with aromatase inhibitors also is associated with decreased bone mineral density, a risk factor for osteoporosis and fragility fractures (28,37). The Hormone and Physical Exercise (HOPE) study examined the effects of an exercise intervention on severity of aromatase inhibitor-induced arthralgia (primary outcome)(14) and bone mineral density (33). The HOPE study was a randomized controlled trial of exercise versus usual care involving 121 postmenopausal women within 0.5 to 4.0 yr of diagnosis of hormone receptor positive stage I to III breast cancer taking an aromatase inhibitor before enrollment. The yearlong exercise intervention engaged participants in a twice weekly supervised resistance training at a local health club with instructions to complete 150 min of moderate-intensity aerobic exercise at home (primarily brisk walking). At the end of the trial, women reported increasing their exercise by 159 min·wk−1 (SD, 136 min·wk−1) and attended 70% of strength training sessions. Women in the exercise intervention had decreased worst joint pain scores and pain severity and interference compared with increased pain in women in the control intervention (P < 0.001) (14).
Further analysis of the HOPE women explored the effect of exercise on body composition and bone mineral density. The women in the exercise group had a 1.4% decrease in percent body fat and a 0.32-kg increase in lean body mass as compared with those in the control group (33). Despite the small magnitude of these changes, the reverse findings were identified in the usual care group as expected for women on aromatase inhibitors. In this way, the exercise program successfully combated the changes typically associated with aromatase inhibitors. Importantly, the HOPE study demonstrated the feasibility of an exercise program in breast cancer survivors with arthralgia and supports referral of this target population to community-based exercise programs, such as LIVESTRONG® at YMCA. Sharing the ways exercise can combat the negative side effects of aromatase inhibitors with patients and providers may help overcome barriers of concern about the ability to engage in physical activity.
Toward the goal of consistent physical activity after breast cancer
Unfortunately, being physically active during times of good health is challenging, and barriers are even greater during times of personal illness. Engaging and remaining engaged in physical activity posttreatment for breast cancer remains particularly challenging for survivors. Despite the importance placed on exercise by organizations, such as the Institute of Medicine (IOM), American Cancer Society, and American College of Sports Medicine, similar rates of breast cancer survivors (10%) participate in physical activity as the general population (8,27,31,35). Henriksson et al. (12) recently studied the perceived barriers to, and facilitators of, exercise during adjuvant cancer treatment. Semistructured focus group and individual interviews were conducted with 23 patients. Three categories were identified: 1) physical and emotional barriers, 2) perspective and attitudes, and 3) support and practicalities. Patients identified physical and emotional barriers to exercise, including the side effects of cancer treatment, comorbid conditions, and emotional distress. Perspectives and attitudes included self-efficacy and self-image, preference of exercise type (i.e., something enjoyable), concerns and expectations about being physically active, experiences with physical activity, and cancer as a “teachable moment.” Patients also identified support and practicalities as both potential barriers and facilitators, including overprotective supports inhibiting physical activity, environmental support and practical issues (i.e., time), motivational support, and strategies to help engage in exercise (12). An improved understanding of the barriers and facilitators specific to patients with cancer can aid in the development of future successful exercise interventions for this important target population.
Motivation plays an important role in being physically active, particularly in patients dealing with the challenge of a breast cancer diagnosis. Courneya et al. (3) studied patient motivation for different types and doses of exercise during breast cancer chemotherapy in a randomized controlled trial. Patients with breast cancer initiating chemotherapy (n = 301) were randomized to a standard dose of 25 to 30 min of aerobic exercise, a higher dose of 50 to 60 min of aerobic exercise, or a combined dose of 50 to 60 min of aerobic and resistance exercise. Despite varying before initiation of exercise program, motivational outcomes after the three interventions were similar. This is an important finding, suggesting that clinicians can recommend any of these exercise programs for patients with breast cancer undergoing chemotherapy (3). Further, higher rates of motivation can be expected to improve rates of continuation and better long-term outcomes for breast cancer survivors.
Despite the many benefits of physical activity after a diagnosis of breast cancer, health care professionals face barriers to promoting exercise. Smith-Turchyn and colleagues (32) conducted a qualitative study with health care professionals who care for breast cancer survivors. Semistructured interviews were conducted with 24 professionals to investigate both the barriers and facilitators of exercise promotion. Five main categories were identified, including: 1) institutional barriers, 2) health care professional barriers, 3) perceived patient barriers, 4) facilitators (resource and service needs), and 5) patient characteristics. Overall, barriers were similar to those identified by health care professionals in general. Institutional barriers reported included limited time with patients and a lack of funding for exercise interventions and appropriate rehabilitation professionals within the institution. Health care professional barriers were similar, including lack of knowledge, low priority, personal limitations, and forgetting to discuss exercise. Perceived patient barriers echoed the findings described above by Henriksson et al., including cost, lack of accessibility, transportation, time, patient side effects and symptoms, and a negative attitude toward exercise. Health care professionals did identify institutional supports as facilitators of exercise promotion, including inclusion of a rehabilitation professional as part of the breast disease site team and exercise programs housed within the institution. Health care professional education and champion leaders were additionally identified as supportive. Individual supports discussed included patient-facing educational materials, such as pamphlets, posters, prescription pads, and handouts (32). These institutional and individual supports are important to note, given that they may be successfully implemented in similar clinical settings with the necessary resources.
Recent and ongoing studies to improve physical activity after breast cancer
Given the limited engagement in physical activity of breast cancer survivors, innovative approaches are needed to successfully engage women in physical activity. Technology-based interventions overcome typical programming barriers, such as distance, time, and cost. Lyons and colleagues (17) currently are conducting the Self-Monitoring Activity: A Randomized Trial of Game-Oriented Applications (SMARTGOAL) study to test a 6-month intervention using narratives and video games as one approach to engage patients. Galiano-Castillo and colleagues (7) conducted a randomized controlled trial evaluating the impact of an Internet-based exercise intervention in breast cancer survivors. The objective of this study was to determine the effectiveness of a telehealth system, an online system that facilitates the development of remote rehabilitation, to improve adverse side effects in breast cancer at 8 and 24 wk. Patients (n = 81) were randomized to the either the intervention or control group, consisting of usual care. The intervention was found to significantly improve the quality of life, pain, muscle strength and fatigue, with results maintained after the 6-month follow-up period (7). These technology-based approaches provide opportunity to determine disseminable, low-cost programming to engage breast cancer survivors in physical activity and keep them motivated over time.
Eakin and colleagues (4) are testing a telephone-delivered healthy lifestyle program for cancer survivors in the Healthy Living after Cancer study. This study is a national dissemination and implementation study to test the integration of an evidence-based lifestyle intervention for cancer survivors into an existing telephone cancer support service delivered in Australia. Patients will receive 12 health coaching calls over 6 months from nurses/allied health professionals with goals to improve physical activity, healthy eating, and weight control. The Healthy Living after Cancer study will target 900 patients over a 3-yr period, providing much-needed practice-based evidence on how best to support cancer survivors (4).
Evidence is convincingly mounting for the benefit of incorporating exercise into breast cancer prevention and treatment. Evidence aside, however, anecdotes of the power of exercise after a cancer diagnosis are persuasive. Dr. Hope, in her article entitled, “A survivor's perspective on the power of exercise after a cancer diagnosis,” described the shock and fear after her diagnosis and how exercise helped her cope, adjust and regain hope throughout her treatment. “It would be a game changer if we could prescribe exercise for patients with cancer and give them the resources they need to be healthier as they navigate treatment” (13).
Significant barriers are faced by both patients for engaging in exercise and health care professionals in promoting exercise. Despite the many benefits of exercise in the prevention and treatment of breast cancer, an inability to successfully engage patient and health care professionals will drastically limit any impact on public health. Therefore, future research is necessary to determine innovative approaches to address and overcome these barriers. Research across disciplinary lines, such as conducted by the National Cancer Institute’s Transdisciplinary Research on Energetics and Cancer (TREC) Centers, has the potential to identify innovative approaches to engaging patients in physical activity for both the prevention and treatment of breast cancer (30).
The authors declare no conflict of interest and do not have any financial disclosures.
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