Physical activity after diagnosis has been linked to decreased risk of recurrence and improved disease-specific and overall survival in breast and colorectal cancer survivors. These data are based on observational studies, including cohort studies of cancer survivors and clinical treatment trials in which participants’ physical activity was measured and a secondary analysis was conducted to investigate the relationship between physical activity and outcomes. In all of these observational studies, physical activity was measured prior to assessment of the outcomes or endpoints.

A review of observational studies showed that breast cancer survivors who engaged in physical activity after diagnosis reduced their risk of breast cancer recurrence and breast cancer-related death compared with survivors who were inactive (Ballard-Barbash et al. 2012). Although one study showed no relationship between leisure time physical activity and breast cancer-related death, four studies have demonstrated a 35–51% reduction in breast cancer-related death among survivors who engaged in leisure time physical activity, and two have shown a trend in favor of reduced breast cancer-related death for those who engaged in leisure time physical activity.

For colorectal cancer, increased levels of physical activity are associated with reduced cancer-specific mortality and overall mortality. In one study of patients with stage III colorectal cancer, activity levels of 18 or more metabolic equivalent hours per week (equivalent to about 6 hours of moderate-intensity walking) were associated with a 47% improvement in disease-free survival rates (Meyerhardt et al. 2006). Observational studies have explored molecular modifiers of this effect, with results showing a relationship between postdiagnosis physical activity and disease-free survival only among colorectal cancer survivors who were positive for tumor alterations of cadherin-associated protein β1 (Morikawa et al. 2011) or whose tumors showed loss of p27 (Meyerhardt et al. 2009).

Exercise and physical activity have a range of other quality-of-life and health benefits for cancer survivors as well. Improvements in quality of life associated with exercise have been demonstrated in multiple randomized clinical trials, most of which compared outcomes in randomized groups of survivors participating in a supervised exercise intervention with outcomes in a control group of survivors who did not exercise or received the intervention after the final assessment.

Speck et al. (2010) published a systematic review of 82 randomized trials of exercise interventions published through November 2009, 66 of which were of sufficient quality to calculate effect sizes. Forty percent of the studies were conducted in patients during treatment and 60% were conducted after treatment. Eighty percent of the studies tested aerobic exercise interventions or aerobic exercise combined with other exercise modalities. Eighty-three percent of the studies involved breast cancer survivors. The exercise interventions, whether provided during or after treatment, were shown to increase physical activity levels, aerobic fitness, and upper and lower body strength, all very salient outcomes in cancer survivors, who are often in a deconditioned state after cancer treatment. Interventions conducted during treatment improved functional aspects of quality of life, anxiety, and self-esteem, and exercise interventions conducted after treatment positively influenced overall quality of life, breast cancer-specific aspects of quality of life, fatigue, self-reported mental confusion, and body image.

Exercise during and after treatment has also been shown to decrease body weight and body fat percentage. A recent Cochrane review of the quality-of-life benefits of exercise in cancer survivors showed that exercise programs improved quality of life in similar domains to those examined in the review by Speck et al. as well as sexuality, social functioning, and sleep disturbance (Mishra et al. 2012). Although the idea that exercise might improve cognitive functioning is intriguing, as has been observed in studies linking exercise in the elderly with improved cognitive functioning, the Cochrane review did not find sufficient evidence to determine whether exercise improved cognitive functioning in cancer survivors (Mishra et al. 2012).

Although only a few trials have examined resistance training interventions, this exercise modality has been shown to positively influence very salient quality-of-life issues in cancer survivors. Schmitz et al. (2009, 2010) conducted a randomized trial of a progressive weight training program for breast cancer survivors. The question of whether weight training is safe and beneficial for breast cancer survivors had been a controversial issue because of concerns that upper body exercise on the survivors’ affected side could increase the risk of lymphedema. Participants in the progressive weight training program (154 of whom did not have lymphedema and 141 of whom had stable lymphedema) attended 90-minute small group sessions supervised by a fitness professional twice per week for 13 weeks. The first sessions started with 2 sets of 10 repetitions using low weight and gradually increased to 3 sets of 10 repetitions, and participants increased the weight if their symptoms did not increase. After the 13 weeks of supervised sessions, participants continued to do the exercises unsupervised twice per week. The intervention increased upper and lower body strength and was found to be safe for both participants with stable lymphedema at baseline and participants who did not have lymphedema. No significant difference was found between the weight training group and the control group in the proportion of patients who experienced a 5% or greater change in limb swelling. Among patients who had lymphedema, participants in the weight training group experienced fewer exacerbations of their lymphedema, and fewer and less severe symptoms, than did participants in the control group (Schmitz et al. 2009).

Exercise can also help improve health and quality of life in cancer survivors through its effects on comorbid health problems. This is important because, with advances in early detection and treatment, many survivors die of diseases other than cancer. In addition, some chronic diseases (e.g., arthritis) may not cause death but can decrease a survivor’s health and physical functioning. Exercise has been shown to reduce the risk of cardiovascular disease and diabetes, as well as improve physical functioning among individuals with chronic conditions such as arthritis.

Obesity may increase cancer survivors’ risk of poor cancer outcomes, including recurrence and cancer-related death, especially among those with breast, prostate, and colon cancer (reviewed by Demark-Wahnefried et al. 2012). However, much of the negative effect of obesity appears to be related to body mass index at diagnosis, and it is unclear whether weight loss after diagnosis improves outcomes. Studies investigating whether weight loss improves outcomes are complicated by the fact that it is often unclear whether the weight loss was intentional or unintentional (e.g., weight loss caused by cachexia may indicate disease progression).

Weight gain is common among breast cancer survivors, and some studies have shown that this weight gain is linked to increased breast cancer-related death. Analyzing data from the Nurses’ Health Study, Kroenke et al. (2005) found that among never-smokers, weight gain after a breast cancer diagnosis was associated with an increase in breast cancer-related death (65% increase among those who gained more than 2.0 kg/m²). Nichols et al. (2009) analyzed a cohort of 3,993 breast cancer survivors and found that among women who gained more than 10 kg, all-cause mortality increased by 70% and breast cancer-related death increased by 78% compared with women whose weight was stable. Other observational studies have not shown a relationship between weight gain and risk of recurrence (Caan et al. 2008), although one study, which analyzed two cohorts of early-stage breast cancer survivors, showed a decreased risk of recurrence in women who lost a moderate amount of weight (5–10%) in one of the cohorts (Caan et al. 2006).

Additionally, findings from the Women’s Intervention Nutrition Study indicated that among hormone receptor-negative breast cancer survivors who were randomized to receive a low-fat diet intervention, relapse-free survival improved by 24% compared with the control group (Chlebowski et al. 2006). The beneficial effect of the intervention may have been related to the weight loss that occurred in the low-fat diet group. In the Women’s Healthy Eating and Living trial, in which breast cancer survivors were randomized to receive a high-fiber, low-fat diet high in vegetables and fruits or no intervention, no weight loss was observed in the intervention group and the intervention did not affect breast cancer event-free survival (Pierce et al. 2007a). However, secondary analyses to explore fruit and vegetable consumption in combination with exercise found that this combination led to a decreased risk of recurrence (Pierce et al. 2007b).

Obesity can also decrease cancer survivors’ quality of life. Studies have shown that obesity in cancer survivors is related to increased fatigue and decreased physical functioning and quality of life (Basen-Engquist et al. 2009; Mosher et al. 2009). For example, in a survey of 753 survivors of breast, prostate, and colorectal cancer, Mosher et al. (2009) found that high body mass index was associated with poor physical aspects of quality of life, including increased pain, decreased physical functioning, increased fatigue, decreased self-perceived health, and increased limitations in fulfilling daily roles because of physical health problems. Studies have shown that weight loss interventions for cancer survivors involving exercise, dietary change, and behavioral techniques have also produced improvements in quality of life, particularly physical functioning (Morey et al. 2009; Basen-Engquist et al. 2010).