The sample size was small and the results not definitive, but authors of a new study on the effects of exercise on women undergoing chemotherapy for breast cancer assert that the findings were strong enough to support the need for further clinical trials.
The Canadian study (abstract only available for free), published ahead of print in Medicine & Science In Sports & Exercise, found increased disease-free survival rates (DFS) among women who had participated in exercise training that began 1-2 weeks after starting chemotherapy. Among 242 breast cancer patients, the 8-year DFS rate for the exercise group was 82.7%, while the control group rate was 75.6%. Authors wrote that the trial "provides the first randomized data to suggest that adding exercise to standard chemotherapy may improve breast cancer outcomes."
The women studied were part of the START Trial, a multicenter study aimed at analyzing differences between aerobic and resistance exercise and their effects on patient-reported outcomes for patients with breast cancer receiving chemotherapy. As part of that trial, participants were divided into 3 groups—an aerobic exercise training (AET) group, a resistance exercise training (RET) group, and a control group that was not required to exercise.
The AET group exercised 3 times a week on a cycle, treadmill, or elliptical ergometer, beginning with 15-minute duration and working up to 45-minute sessions by week 18. RET group participants began by performing 8-12 repetitions of 9 exercises at 60% to 70% of their 1-repetition maximum, increased by 10% each time they completed more than 12 repetitions.
When researchers looked at survival differences among the exercise and nonexercise groups, they found effects that "appear to be meaningful," including combined survival differences between 7% and 9%, with the strongest effects in women who were overweight or obese, had stage II/III cancers, had ER or HER2 positive tumors, or received taxane-based chemotherapies. Authors did not explore the degree of difference between the 2 exercise approaches due to small sample sizes.
Authors cited 3 possible reasons for the positive effects: the possibility that exercise improves the rate of chemotherapy completion, the possibility that it assists in "drug distribution" through changes to metabolism, or that exercise "provides an additive benefit beyond current chemotherapy drugs mediated by mechanisms unrelated to interaction effects."
Although encouraged by the study, authors described the sample size as "clearly underpowered for any definitive conclusions" and pointed out that confidence intervals were wide enough to not preclude the possibility that exercise could produce adverse effects on cancer outcomes. Arriving at "definitive efficacy information" was not the goal of the study, they write, which was meant to "identify promising experimental regimens that have a high likelihood of success" in a subsequent research phase.
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