“We’ve got to do a better job of getting better data,” session chair Lee Jones of the Memorial Sloan Kettering Cancer Center said. “We don’t even know to date if exercise has any efficacy in terms of anticancer benefits.”
In a review of the existing epidemiologic literature in this area, Christine Friedenreich of the University of Calgary, Canada, pointed to 10 studies on breast cancer patients, six studies involving colorectal cancer patients, and three studies on prostate cancer patients, which collectively provide “very strong evidence” of an antitumor benefit of physical activity, she said. However, these studies relied almost exclusively on subjective measures of exercise and failed to control for a variety of confounding factors, such as prediagnosis activity levels, sedentary behavior, and competing risks of mortality. Friedenreich outlined two ongoing studies, the AMBER study and the RUBY study, which aim to correct for these shortcomings in cohorts of 1,500 and 1,200 newly diagnosed breast cancer patients, respectively. “We’re still very much at an early stage in understanding how physical activity is related to cancer survival,” she said. “There’s some very positive and intriguing results to date but there’s a lot of work that can still be done.”
Mark Dewhirst of Duke University in North Carolina focused on work investigating the effects of exercise in mouse models of cancer during his AACR talk. Unfortunately, he noted, among 53 papers on the topic, he found “tremendous heterogeneity,” making it “hard to come up with any kind of consistent pattern.” Still, several studies individually point to a positive effect of physical activity on tumor progression in mice, he noted. In one study, “exercise worked as well as chemotherapy,” Dewhirst said, and the combination of chemotherapy and exercise had even better outcomes.
Animal research allows scientists to probe the potential mechanisms underlying the effects of exercise on cancer outcome. Exercise appears to increase vascular profusion, and to result in more mature vasculature, Dewhirst noted. In addition, studies on animals have found a decrease in cellular oxygen consumption, possibly related to an increase in apoptosis. Taken together, it’s not surprising, then, that tumors in these animals experienced decreased hypoxia.
Going forward, Jones emphasized the need for a more traditional approach to studying the role of exercise in cancer. Even though this sort of intervention is not regulated by the US Food and Drug Administration (therefore, preclinical data are not needed to begin human trials), research efforts could be more fruitful if scientists used epidemiologic results to inform preclinical testing, which in turn could help guide the design of clinical trials. “An adoption of a translational approach, just like we do in the drug world, is absolutely essential,” Jones said.