Exercise Might Improve Survival in Breast and Colon Cancer
“Not surprisingly, physical activity is associated with improved overall survival; it has also been shown for many other diseases, like heart disease, hypertension, and diabetes,” lead author Rachel Ballard-Barbash, MD, MPH, from the division of cancer control and population sciences at the National Cancer Institute (NCI) in Bethesda, Maryland, said in a interview with Medscape Medical News.
The literature review also uncovered evidence from randomized controlled trials that physical activity might favorably alter insulin and insulin-related growth factors, inflammation, and possibly immune function, all of which can influence cancer pathology. “We can’t make any strong conclusions because of the relatively limited number of studies, but this is a promising area for future research,” said Dr. Ballard-Barbash.
The study was published online May 8 in the Journal of the National Cancer Institute.
The study breaks new ground, according to Edward L. Giovannucci, MD, ScD, from the Department of Nutrition at the Harvard School of Public Health, Boston, Massachusetts, in an accompanying editorial.
“Unlike previous reviews, which focused on functional health and quality of life, this review addressed the more provocative question of whether physical activity can actually improve cancer-specific survival,” Dr. Giovannucci writes.
He appreciates that physical activity might help cancer survivors live longer with a better quality of life — a rare combination.
“Many treatments may increase survival, but at a cost of quality of life; physical activity may not only extend life but may also enhance its quality,” Dr. Giovannucci notes. He believes that exercise should be recommended to all cancer patients.
“Even though direct effects of physical activity on cancer are not definitely proven, given that physical activity is generally safe, improves quality of life for cancer patients, and has numerous other health benefits, adequate physical activity should be a standard part of cancer care,” he writes.
The United States is currently home to an estimated 13.8 million cancer survivors. With advances in cancer screening and treatment, cancer survivors are living longer and often seek information about how lifestyle factors can influence their prognosis.
Using the MEDLINE database, Dr. Ballard-Barbash and colleagues identified and systematically reviewed 45 studies (observational and randomized controlled trials) that examined the relation between physical activity and mortality and/or cancer biomarkers in cancer survivors.
The studies were published from 1950 to 2011. This area of research is “relatively new,” the investigators say. “We were surprised to see how rapidly this research area has grown,” said Dr. Ballard-Barbash. “What is striking is that in the observational area, there were 27 studies and almost all of them [were published] after 2005,” she explained.
Evidence Best for Breast and Colon Cancer
The strongest evidence is for breast cancer survivors, with “fairly consistent evidence” from observational studies that physical activity either before or after a breast cancer diagnosis is associated with a reduction in both breast-cancer-specific mortality and all-cause mortality. This risk reduction is statistically significant, and ranges from 41% to 51% in nearly half the studies. There is also some evidence in breast cancer studies of a dose–response effect in which risk reduction increases with increased activity levels, the investigators report.
The next strongest evidence is for colorectal cancer, with statistically significant reduced risks for colorectal-cancer-specific mortality ranging from 45% to 61% in several studies. Physical activity after diagnosis was also associated with reduced risk for death from any cause; several studies reported statistically significant reductions ranging from 23% to 63%. In the colorectal cancer studies, there is also evidence of a dose–response relationship.
In their paper, Dr. Ballard-Barbash and colleagues note that the evidence on colorectal cancer is “sufficiently compelling” to justify the first-ever randomized exercise intervention trial among colon cancer survivors. The multicenter Colon Health and Life Long Exercise Change (CHALLENGE) trial is being conducted in Canada and Australia with 963 survivors of stage II or III colon cancer.
For other cancers, the evidence is still insufficient to make any conclusions about the “strength, consistency, and dose–response relationship between physical activity and cancer survival,” the investigators write. “We found only 1 study in prostate cancer, 2 in ovarian cancer, and 1 in brain cancer,” Dr. Ballard-Barbash noted.
More Study a High Priority
The investigators caution that, given the “diverse methods” used in these studies to assess physical activity, it is not possible to extrapolate specific recommendations from the findings regarding the exact type, dose, and timing of physical activity required to reduce mortality after a cancer diagnosis.
Nonetheless, they say that physical activity is “safe for cancer survivors, has proven physical and mental health benefits, is recommended by both the [American College of Sports Medicine] and American Cancer Society, and may also improve survival after cancer, but additional research is warranted before clear conclusions can be reached on the effects of physical activity on disease outcomes among many groups of cancer survivors.”
Dr. Giovannucci concludes that “given the promise of a role of physical activity in reducing cancer-specific mortality, future research involving observational studies, interventions, and mechanistic studies should be a high priority. Few other leads have shown as much promise as physical activity in extending the lives of cancer survivors.”
The study authors and Dr. Giovannucci have disclosed no relevant financial relationships.
J Natl Cancer Inst. Published online May 8, 2012. Abstract, Editorial