Boston: Exercise can substantially reduce the risk of death following a diagnosis of colorectal cancer, two new studies confirm, both published in this month’s Journal of Oncology.

In one study, Dr. Jeffrey A. Meyerhardt, from Dana Farber Cancer Institute in Boston, and his team identified 573 women diagnosed with stage I, II, or III colorectal cancer. During a median follow-up of 9.6 years, 132 women died; 80 of these deaths were due to the cancer.

The investigators documented the level of physical activity the participants reported following their diagnosis, and translated that to “metabolic equivalent tasks” (MET-hours per week). For example, walking at a rate of 2.9 mph was assigned a score of 3 MET-hours, aerobic exercise was given a 6, and running faster than 10 min/mile was counted as 12 MET-hours.

After adjusting for multiple confounders, the authors observed that compared with patients who reported less than 3 total MET-hours per week of activity, those reporting 18 or more MET-hours per week were significantly less likely to die of their cancer or of any cause.

In another study, Meyerhardt’s team studied 832 patients with advanced colon cancer who underwent surgery and chemotherapy with “curative intent.” The subjects reported their recreational physical activities approximately 6 months after their treatment had ended.

During median follow-up of 2.7 years, 159 patients had cancer recurrence and 84 died.

Compared with patients exercising less than 3 MET-hours, those who exercised 18 to 26.9 MET-hours per week were less likely to die in adjusted analyses, similar to the other study.

In a related editorial, Dr. Wendy Demark-Wahnefried, from Duke University Medical Center in Durham, North Carolina, notes that these two studies report outcomes similar to those of a previous study in which activity after a diagnosis of breast cancer was also associated with survival.

But all three trials were observational, she points out. So before physicians can be absolutely sure that exercise prevents progression or recurrence of cancer, randomized, controlled trials will be required.

Furthermore, important questions remain unanswered, she added, such as the safety of exercise for patients who have been given therapy toxic to the heart, what exercises are most beneficial, and which patients are most likely to benefit.