Colorectal cancer risks: tobacco, obesity and inactivity

Todd S. Crocenzi, M.D.
Medical director, Gastrointestinal Cancer Research Program
Robert W. Franz Cancer Research Center in the Earle A. Chiles Research Institute

Published April 2010

Tobacco use and sedentary lifestyle, along with its close cousin, obesity, are risk factors for colorectal cancer. Modifying these risks also complements the efforts of our colleagues in primary care, cardiology and pulmonology, to name a few. We can’t go wrong here.


Tobacco use found itself once again firmly established as a cause of cancer; this time, colorectal cancer, according to findings reported from the American Cancer Society (L.M. Hannan, et al., Cancer Epidemiol Biomarkers Prevention, 2009;18(12):3362–7).

This publication along with other cumulative evidence prompted the International Agency for Research on Cancer to upgrade its causality designation of smoking and colorectal cancer from “limited” to “sufficient.”

Like other lifestyle modifications, I truly believe the impact that health care providers can make in convincing our patients to change is rooted in our own actions. There’s nothing more convincing than a positive example.

Physicians, at least in the United States, have gotten smarter over the past 30 years and the prevalence of smoking among physicians has dropped dramatically.

Smoking continues to be more common among nurses. (Next question: Why are any physicians or nurses still smoking?) Of course, tobacco-cessation efforts also can be augmented through positive messages from our world leaders, tobacco taxes, tobacco-free policies and funding for successful tobacco-cessation programs, particularly for the uninsured or underinsured.

Each of us can’t change everything, but each of us can do something, such as ensuring our offices enhance the “stop smoking” message by identifying patients under our care who smoke, reinforcing cessation at every visit and promoting the benefits of programs with a record of success (Oregon Tobacco Quit Line, 1-800-QUIT-NOW).

Health system actions such as Providence Health & Services’ smoke-free campus efforts help emphasize how high a priority tobacco cessation remains. The medical community can continue to find common ground with this issue; a modern health care system with a quarter of its workforce still smoking is shameful.

Sedentary lifestyle and obesity together represent perhaps more daunting lifestyle risks than tobacco use. Cancer, particularly colorectal cancer, is more common among individuals with these lifestyle patterns. Accumulating evidence suggests that control of body weight can reduce risk for colon cancer as well as for breast cancer in the primary and secondary prevention arenas.

The challenges of obesity treatment as a strategy to reduce cancer risk deserve attention, including developing better therapeutics, better definition of treatment goals and validating sustainable therapy plans. However, data suggest that if we start now and just get our patients moving, those individuals may carry a lower risk of colorectal cancer (K.Y. Wolin et al, British Journal of Cancer 2009; 100, 611–616).

The meta-analysis of 52 studies (both case-control and cohort studies) revealed an inverse association between physical activity and colon cancer, with an overall relative risk (RR) of 0.76 (95 percent confidence interval (CI): 0.72, 0.81) or a 24 percent risk reduction in colorectal cancer.

The benefit spanned across studies that included both occupational and leisure-time activity. The meta-analysis did not yield a best prescription for exercise; however, earlier epidemiologic studies suggest that walking at least a few hours a week can make a difference. I encourage patients to make exercise part of their daily routine.

While some interesting abstracts were presented at the annual 2010 Gastrointestinal Cancers Symposium (aka “ASCO GI”) in January with regard to improvements in screening for early detection, very little was presented regarding prevention. However, interest remains in difluoromethylornithine (DFMO) as a seemingly well-tolerated chemopreventive agent. DFMO continues to fly under the radar, having been developed over 20 years ago. It inhibits ornithine decarboxylase, the first enzyme in polyamine synthesis, shown to be important in carcinogenesis. Perhaps fewer polyamines around would mean less colorectal cancer.

Exploring the mechanism of this proposed chemopreventive agent, Kashyap Raj, M.D., presented an interesting analysis of colorectal cancer risk and polyamine-rich diet (abstract No. 279) culled from a phase III prevention trial of DFMO and sulindac.

The data suggested avoidance of polyamine-rich foods such as orange juice, meats, green peas and corn among others may reduce risk of colorectal cancer. I look forward to further work in this area.

Cancer awareness months, such as March for colorectal cancer, call us to take a moment, review what we know and ask ourselves, what are we going to work on tomorrow? Yes, we need to continue to find ways to detect and cure cancer, as well help those unfortunate enough to find themselves with advanced disease. Ultimately, success in colorectal cancer will be determined by how well it’s prevented.

Clinical articles by Todd S. Crocenzi, M.D.