More than 1.2 million Americans were expected to be diagnosed with invasive cancer in 2000 (1). Over their lifetime, Americans have a ˜ 41% probability of developing cancer, with nearly 80% of all cancers being diagnosed in persons aged ≥ 55 yr (1). Early detection and improved treatments for cancer have resulted in increased survival rates, with the current 5-yr relative survival rate (adjusted for normal life expectancy) estimated to be ˜ 60% (1). Increased incidence rates and improved survival rates have resulted in more than 8.4 million Americans being alive today who have a history of cancer.
Unfortunately, surviving cancer usually means enduring significant and prolonged medical treatments. The three primary cancer treatments are surgery, radiation therapy, and systemic therapy or chemotherapy (i.e., drug therapy). Increasingly, sequential combinations of the main cancer treatment modalities (i.e., surgery, radiotherapy, and systemic therapy) are being used to treat cancer.
CANCER AND QUALITY OF LIFE
Quality of life (QOL) can be defined as overall happiness and satisfaction with life (7). There is a general consensus that QOL is composed of multiple dimensions of well-being, including physical, functional, cognitive, emotional, social, and spiritual dimensions (7). Not surprisingly, cancer and its treatments can result in significant reductions in many different QOL-related outcomes. Some of the more common emotional and social sequelae of the cancer experience include depression, anxiety, body image concerns, decreased self-esteem, loss of a sense of control, and social isolation. The physical and functional effects of cancer treatments may include low blood counts, asthenia, reduced cardiovascular and pulmonary function, muscle weakness and atrophy, weight change, difficulty sleeping, fatigue, nausea, vomiting, and pain. Although the side effects tend to peak during treatment, therapy-related symptoms may persist months or even years after treatment. Not surprisingly, research has also shown that cancer patients significantly reduce the amount of exercise they perform during treatment (Figure 1).
EXERCISE AND QUALITY OF LIFE AFTER CANCER DIAGNOSIS
The majority of research on exercise after cancer diagnosis has focused on cancer survivors (i.e., persons who have completed medical treatment and are considered “cured”) (2). The primary foci of such interventions are rehabilitation and health promotion. Exercise interventions for cancer patients (i.e., persons currently receiving medical treatment), however, are based on a coping model. In a coping model, exercise is viewed as a way of mitigating the common side effects or symptoms of cancer treatment. Implementation of the exercise intervention coincides with the treatment regimen rather than occurring after treatment has been completed.
Exercise may influence QOL during cancer treatment in many different ways. Figure 2 provides a simple organizational model on how exercise might ultimately enhance QOL during cancer treatment. First, exercise may alter one of the many hypothesized biopsychosocial mechanisms thought to underlie improved coping and adjustment to cancer (e.g., fitness, self-efficacy, social interaction). In turn, changes in these biopsychosocial mechanisms may alleviate or prevent the occurrence of many of the common symptoms associated with cancer and its treatments (e.g., fatigue, insomnia, pain, anorexia). Amelioration of these symptoms may then reduce their impact on, or level of interference with, the ability to perform activities of daily living, leisure activities, interactions with others, and so on. Finally, enhanced physical and social activities may improve psychological distress/well-being (e.g., anxiety, depression), thereby improving overall QOL.
The purpose of the present article is to provide a comprehensive and systematic review of the literature on exercise interventions during cancer treatment. The primary hypothesis of this review is that exercise during cancer treatment will have beneficial effects on a wide variety of outcomes that may enhance QOL.
A literature search was conducted using the CD-ROM databases CancerLit, CINAHL, Heracles, MEDLINE, PsycINFO, and SPORT Discus. Key words that related to cancer (i.e., cancer, oncology, tumor, neoplasm, carcinoma), the postdiagnosis time period (i.e., rehabilitation, therapy, adjuvant therapy, treatment, intervention, palliation), and exercise (i.e., exercise, physical activity, physical therapy, sport, weight training) were combined and searched. Relevant articles were then hand searched for further pertinent references. To be included in the review, studies had to examine the effects of an exercise intervention during cancer treatment. Descriptive studies and studies that examined exercise interventions after treatment were excluded. Cancer treatment was defined as the time period between treatment initiation and either (a) 1 wk after the last radiation treatment, (b) 3 wk after the last intravenous chemotherapy treatment, or (c) 3 wk after the cessation of hormone therapy. This definition allowed time for the acute residual effects of treatment to dissipate before the person is considered to be posttreatment. Exercise interventions that did not substantially overlap with the treatment time period were excluded. Space limitations and restrictions on the number of references also resulted in the exclusion of studies that examined movement therapy or stretching/flexibility exercises aimed at improving range of motion. Nevertheless, it is acknowledged that such interventions could ultimately enhance QOL in cancer patients. Finally, studies that did not disentangle the effects of exercise from a multiple intervention package (e.g., exercise combined with diet, social support, psychosocial counseling, etc.) were also excluded. Overall, 11 studies (3–6,8–14) met the selection criteria (Table 1).
Five of the 11 studies examined early-stage breast cancer patients receiving chemotherapy, and three studies examined mixed cancer patients after high-dose chemotherapy and bone marrow/stem cell transplantation. One study each examined breast cancer patients receiving radiation therapy, prostate cancer patients on hormone therapy, and mixed cancer patients experiencing severe fatigue on mixed treatments. Study designs consisted of four randomized clinical trials (RCTs) with usual-care or wait-list controls, two RCTs with placebo (i.e., stretching) and usual-care controls, one RCT comparing two exercise frequencies (i.e., 3 versus 5 d per week) with usual-care controls, one pretest-posttest design with two matched controls (i.e., nonexercising cancer patients and exercising healthy persons), and three pretest-posttest designs with no controls. The sample sizes ranged from 5 to 70 with a mean of 33. Supervised exercise programs were reported in nine studies, whereas two studies reported unsupervised, home-based exercise programs. Nine studies tested an aerobic exercise intervention (six cycling, two walking, and one self-selected), whereas two studies examined resistance training. All studies followed traditional exercise prescription guidelines in terms of frequency, intensity, and duration of exercise, but the length of the intervention was ≤12 wk in all of the studies and < 10 wk in six of the studies. The studies examined a wide variety of biopsychosocial outcomes, with the most common being functional capacity (seven studies). Three studies each examined body composition, mood states, and fatigue.
Overall, the results of these studies consistently demonstrate that an exercise intervention during cancer treatment has many positive effects. In fact, all 11 studies showed statistically significant results in favor of the hypothesis despite small sample sizes. The physical and functional benefits that have been demonstrated include improvements in functional capacity, muscular strength, body composition, hematological indices, sleep patterns, nausea, fatigue, pain, and diarrhea. The psychological and emotional benefits that have been demonstrated include positive changes in personality functioning, body satisfaction, mood states (including anxiety, anger, and depression), and general QOL.
Results of the reviewed studies are promising and suggest that exercise during cancer treatment may improve many biopsychosocial outcomes. The primary foci of these studies, however, has been on the biologic mechanisms that may underlie improved QOL (e.g., physiological and functional fitness), actual symptom occurrence (e.g., fatigue, pain, sleep), and psychological distress (e.g., depression, anxiety). Very little research has addressed the possible psychosocial mechanisms by which exercise might improve QOL (e.g., self-efficacy, distraction, sense of accomplishment), the impact of symptom occurrence on functional and social well-being, positive indicators of psychological well-being (e.g., energy, pride, hope), or actual QOL itself. Moreover, the few studies that did assess multiple outcomes (e.g., biologic mechanisms, symptom occurrence, psychological distress) did not examine the interrelationships among the outcomes and, consequently, can be considered descriptive or atheoretical. In such studies, it is not clear whether changes in the biologic mechanisms were responsible for the changes in symptom occurrence and, in turn, whether changes in symptom occurrence were responsible for changes in psychological distress. Future studies should adopt a theoretical framework for determining the effects of exercise on QOL during cancer treatment.
Methodologically, the studies were generally rigorous, consisting of RCTs with appropriate controls, supervised exercise sessions, an appropriate exercise stimulus, objective fitness indicators, and validated psychometric scales. The primary methodological limitations of the current research, however, include (a) small convenience samples, which restrict the generalizability of the findings; (b) relatively short exercise interventions that did not coincide with the medical treatment in its entirety; and (c) limited follow-up.
Despite the descriptive nature and methodological limitations of the current research, the major concern at this time is simply the nascency of the field. That is, research has just begun on this issue and much more remains to be done. One important future research direction is to extend the research beyond breast cancer to other major cancers (e.g., prostate, colorectal, lung) and beyond chemotherapy to other major cancer treatments (e.g., radiation therapy, hormone therapy). Each cancer/treatment combination is unique based on a different demographic profile of the patients, pathophysiology of the disease, treatment protocol, and side effects. Consequently, it would be unwise to generalize the benefits of exercise found for one particular cancer/treatment combination to another.
A second important future direction is to initiate “second-generation” studies in the one area where sufficient research has demonstrated reliable results—early-stage breast cancer patients receiving chemotherapy. The studies reviewed here may be thought of as first-generation studies because they have compared a single exercise intervention with nothing at all. Second-generation studies are needed to determine the optimal type (e.g., aerobic versus resistance exercise training), volume (e.g., moderate versus high intensity), and context (e.g., individual versus group based) of exercise for enhancing QOL in early-stage breast cancer patients receiving chemotherapy. Moreover, second-generation studies are also needed to compare and integrate exercise with other currently accepted QOL interventions (e.g., group therapy, diet, social support) to determine whether exercise is complementary or redundant with these interventions in such patients.
A third important, although controversial, future direction is to determine whether exercise after the diagnosis may influence tumor growth, disease progression, recurrence, and/or survival from cancer. From a primary prevention perspective, exercise has been shown to reduce the risk of certain cancers (e.g., colon, breast), and the mechanisms thought to confer this reduced risk (e.g., hormonal changes, immune function, obesity) may also operate in the secondary prevention of cancer. Moreover, additional mechanisms may operate after the diagnosis, such as highly fit individuals being able to complete more dose-intensive cancer treatments.
Finally, the effectiveness of exercise as a QOL intervention during cancer treatment will depend to a large extent on the motivation and ability of participants to adhere to such a program. Exercise adherence is a major challenge for health professionals regardless of the demographic profile of the group or the purpose of the exercise. The significant complications caused by cancer and its treatments make it likely that exercise adherence is even more difficult for cancer patients. Consequently, understanding the demographic, disease/medical, and social cognitive determinants of recruitment and adherence to various types of exercise programs in cancer patients is an important adjunct to this line of research. Similar to outcomes research, however, it is likely that different determinants of exercise will emerge for the different combinations of cancers and treatments.
SUMMARY AND CONCLUSION
More than 8 million Americans are alive today who have been through the cancer experience, and this number is increasing. Moreover, cancer treatments are intensive and cause significant complications that result in acute reductions in many QOL-related outcomes. Based on a review of 11 methodologically sound studies, it was concluded that exercise during cancer treatment is likely to be beneficial to cancer patients. Future research is needed, however, because this field is only beginning to take shape.
Dr. Courneya’s research program is supported by the National Cancer Institute of Canada (NCIC) with funds from the Canadian Cancer Society (CCS) and the CCS/NCIC Sociobehavioral Cancer Research Network.
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