The results of two new prospective, observational studies offer compelling evidence to suggest that regular physical activity in the months following treatment may decrease the risk of cancer recurrence and death from colorectal cancer.

In the studies, patients with early- to later-stage colorectal cancer (but not distant metastases) who engaged in regular activity after diagnosis decreased the likelihood of cancer recurrence and mortality by 40 to 50 percent or more compared with patients who engaged in little to no activity.

Released early online July 5 in the Journal of Clinical Oncology, the studies' results held true regardless of physical activity levels before cancer diagnosis or other factors that predict recurrence risk, such as the number of nearby lymph nodes harboring cancer cells.

The results, said the studies' lead author, Dr. Jeffrey A. Meyerhardt of the Dana-Farber Cancer Institute, may offer some important insight into why some colorectal cancer patients who receive standard-of-care treatments, including surgery and adjuvant chemotherapy, have recurrences, and some don't.

"One assumption has always been that it must be something about the molecular makeup of their tumor," he said. "This study implies that there are some lifestyle factors that may also have a significant effect on [treatment] outcomes."

The first study involved 832 patients with stage III colorectal cancer who participated in a clinical trial led by the Cancer and Leukemia Group B cooperative group that compared two adjuvant chemotherapy regimens.

On two occasions - 4 months after having their tumors surgically removed and then again 10 months later, well after adjuvant therapy was completed - participants provided detailed information about their diet and physical activity via a self-administered questionnaire. Only data from the second questionnaire were considered in the analysis.

Researchers converted the reports of physical activity (ranging from jogging to flights of stairs climbed) to metabolic equivalent task (MET) hours. For example, walking at a moderate pace for an hour is equivalent to 3 MET hours.

Compared with patients who reported less than 3 total MET hours per week, those reporting 18 to 26.9 and 27 or more had their risk of death from colorectal cancer reduced by 49 and 45 percent, respectively. In other words, 6 or more hours a week of walking at a moderate pace showed clear benefits.

The second study followed a cohort of 573 participants in the long-running Nurses' Health Study who, during the course of the study, were diagnosed with colorectal cancer.

Compared with participants who reported less than 3 MET hours of activity per week, those reporting 18 or more had their risk of death from colorectal cancer cut by 61 percent and their risk of death from any cause reduced by 57 percent.

In an accompanying editorial, Dr. Wendy Demark-Wahnefried of Duke University Medical Center noted that the risk reductions seen in these studies - as well as strikingly similar results reported last fall from a study of women with early-stage breast cancer - parallel "that of trastuzumab (Herceptin) for HER 2-positive breast cancer patients."

Dr. Julia Rowland, head of the NCI Office of Cancer Survivorship, Division of Cancer Control and Population Sciences (DCCPS), called the new studies "an important finding that adds to the evidence base on physical activity and cancer outcomes.

"They suggest that the time may be ripe to launch a randomized clinical trial of physical activity after cancer treatment," she continued. "To me, it opens up the door to an incredible wealth of science that, among other things, could help explain things like the interplay between behavior and underlying tumor processes."

NCI officials have already held preliminary discussions about the best settings for such a trial, she added, and how it might be designed.

By Carmen Phillips