This review summarizes the best available evidence regarding the effects of exercise on quality of life and physical outcomes for breast cancer patients and survivors.
Only 3 studies provided adequate data to assess quality of life. The pooled estimate showed that a statistically significant increase of greater than 4.0 points on the FACT scale represents a clinically meaningful improvement in quality of life from exercise.42
Additionally, analyses of the physical functioning and physical well-being subscales of quality of life indicated large improvements (effect size = 0.84) from exercise.
The pooled results of 3 studies examining peak oxygen consumption from symptom-limited graded exercise testing showed an improvement of 3.39 mL/kg per minute or almost one metabolic equivalent (MET) improvement in fitness.43
Each 1 MET increment in fitness has been found to correspond to a 12% improvement in survival in men.43
Since cardiorespiratory fitness is an important predictor of all-cause mortality in women,9
it is possible that an improvement of this magnitude would have similar implications in women; however, the duration of these studies was insufficient to provide firm evidence.
The pooled results of the 6 studies examining the effect of exercise on symptoms of fatigue showed a moderate-to-large effect (effect size = 0.72); however, statistically significant improvements in symptoms of fatigue were reported in only 2 studies.18,34
Both studies examined exercise following primary cancer treatment.18,34
During adjuvant cancer treatment, no effect of exercise on fatigue was found. The evidence suggests that exercise has a nonsignificant and potentially small effect on symptoms of fatigue for women undergoing adjuvant cancer treatment. Despite statistical nonsignificance in the 4 studies, all point estimates were in favour of exercise, which suggests the need for more research before rejecting this effect.
There was no statistically or clinically significant change in body weight or BMI as a result of the exercise trials included in this review. It is not known, however, whether positive changes in body composition occurred as a result of the exercise intervention because there was a lack of studies using direct measures of tissue and body composition. As an example, Schmitz and associates examined body composition by means of dual x-ray absorptiometry and reported positive changes in lean body mass as well as significant decreases in percent body fat in favour of the exercise intervention ().35
As well, Schwartz and colleagues assessed bone density of the lumbar spine using dual x-ray absorptiometry and reported that subjects participating in weight-bearing aerobic exercise had significantly less bone density loss than control subjects ().36
This suggests that positive changes in body composition may occur despite nonsignificant changes in body weight and BMI.
The 14 studies included in this review were of variable quality, and only 4 were considered to be of high quality. Our conclusions are tempered by this fact. Clearly, further progress must be made to improve research quality. Future trials should focus on adequate randomization, concealment of allocation and blinding of outcome assessors throughout the study.
A noteworthy feature of trials included in this review was the wide variability in study interventions. Many different exercise regimens were prescribed. The diversity in exercise prescription is not surprising, given the lack of consensus on the optimal exercise prescription for this patient population. Conversely, the wide variety in study outcomes and measurement methods is surprising. This variation precluded pooling studies and made overall conclusions regarding the relative effectiveness of exercise difficult. The short duration or complete lack of follow-up data examining the effect of exercise on quality of life and rehabilitative outcomes in the long term is also noted. Moreover, data are lacking to support the use of exercise in preventing cancer recurrence and improving overall survival.
A further limitation is the nonspecificity with respect to the timing of the exercise intervention. Clinical heterogeneity was evident, particularly in trials carried out during adjuvant cancer treatment. This resulted from trials in which the participants were undergoing one of a variety of adjuvant treatments (e.g., chemotherapy, radiation therapy and hormonal therapy).
Finally, poor adverse event reporting in most of the studies limits any conclusions about the relative safety of exercise, and the small samples provide insufficient power to detect meaningful differences in rates of rare adverse events. For example, lymphedema is a potential side effect of cancer treatment and represents a barrier to exercise for some patients,4
yet none of the included studies formally monitored for this side effect.
The evidence suggests that exercise is an effective intervention to improve quality of life, cardiorespiratory fitness, physical functioning and symptoms of fatigue in breast cancer patients and survivors. Although these preliminary results are promising, the findings are based on a relatively small number of trials with significant methodologic weaknesses. Furthermore, there is currently no evidence to support the use of exercise regimens to reduce body weight or BMI. On the basis of our findings, we make the following research recommendations:
1. Methodologically rigorous studies designed to examine different exercise regimens (e.g., moderate v. low-intensity) are needed to better understand the role of physical exercise among breast cancer patients and survivors.
2. The exercise prescription should be reported in detail (frequency, intensity, time and type of exercise) to allow for determination of exercise dose–response. To this end, adherence to exercise should be reported for both completion of exercise sessions (attendance) and exercise prescription (intensity and duration). Furthermore, monitoring of activity in the comparison group(s) is necessary to assess potential contamination.
3. Consensus is required on standardized methods of assessing physical fitness and body composition to allow for pooling of data and for comparisons across studies.
4. Future trials should formally monitor for, and report the incidence of, potential adverse events such as lymphedema.