Colorectal Cancer: Understanding the Risks

Cancer is the 2^nd leading cause of death among American men and women, exceeded only by heart disease. The American Cancer Society (ACS) recently released its cancer statistics for 2001. They estimate more than 1.2 million new cancers (incidence) in the U.S. this year and, of these, 135,000 new cases of colon and rectal cancer (CRC). Expected statistics for CRC in the mid-Atlantic region are displayed in Figure 1.

The number of new cases of CRC began to decline in 1985. Decreases in CRC incidence as well as mortality are evident for men and women of all races. The survival rates for CRC are highest if it is found very early. Unfortunately, only 7% of CRC cases are diagnosed early. To prevent CRC, it is important to know the risk factors and obtain regular screening examinations.

Risk Factors

Age: Colorectal cancer is generally a disease of older adults. The risk for CRC begins to rise around age 40 and gradually increases. Ninety-three percent of CRC are diagnosed in people aged 50 years and older. Though age is a factor we cannot avoid, living a healthy lifestyle as one ages may be important to CRC prevention.

Family History: We are rapidly gaining knowledge about who develops CRC. As Figure 2 shows, the majority of CRC, 65% to 85%, occur in people with no known cause (i.e., they are considered sporadic). 10% to 30% of CRC cases occur in people who have a family member who has had a polyp or colorectal cancer. A small percentage of CRC occurs as part of an inherited syndrome. Approximately 5% are associated with hereditary nonpolyposis colorectal cancers (HNPCC) and 1% are associated with familial adenomatous polyposis (FAP). Less than 0.1% are rare CRC syndromes.

Diet: Evidence suggests that diet may be important in reducing one’s risk for colorectal cancer. Perhaps 1/3 of cancer deaths may be related to diet. A high calorie, high fat diet, particularly high in animal fat and protein may increase CRC risk. Alcohol should be limited to 1-2 drinks per week. A low intake of calcium and dietary fiber, particularly from vegetables, is also associated with higher rates of colorectal cancer. Experts recommend consuming at least 5 fruits and vegetables each day. Although antioxidants are hypothesized to prevent cancer, a randomized controlled trial of antioxidant vitamins (beta carotene, vitamin C, vitamin E) has shown no effect on CRC incidence.

Exercise: A sedentary lifestyle has been associated in some but not all studies of an increased risk of colorectal. Moderate daily activity for 20-30 minutes can burn calories, reduce weight and possibly reduce one’s CRC cancer risk.

Cigarette Smoking: In a recent study of more than 750,000 men and women (JNCI, 2000; 92:1888-1896), researchers concluded that CRC death rates were lowest among people who had never smoked, intermediate among ex-smokers, and highest among current smokers. Women who smoked were more than 40% more likely to die from CRC than women who never smoked. Male smokers had more than a 30% increase in risk for dying compared with men who never smoked.

Prevention, the Hope for the Future

Promising research is underway to explore ways to reduce one’s risk for CRC. Observational studies of average-risk people have suggested that the use of some drugs and supplements (nonsteroidal anti-inflammatory drugs (NSAIDs [drugs like aspirin and ibuprofen], estrogens, folic acid, and calcium) might prevent the development of colorectal cancer. To date, none of the evidence has led experts to recommend these drugs and supplements specifically to prevent CRC.

Screening: Today’s Best Strategy

Regular screening is the key to early detection and prevention. Recommendations for regular screening are described in the article “ACS Colorectal Cancer Screening Guidelines 2001: Individuals at Average Risk.” New research in this area is promising. A recent report in the journal Gastroenterology (2000; 119:1219-1227) suggests that the key to painless, noninvasive early detection could be as simple as examining stool samples for DNA changes. Researchers have found that cancers and polyps shed their cells into the fecal material as it passes through the colon. Stool samples from patients with CRC, adenomas (precancerous polyps), and no cancer were examined and showed DNA changes in 90% of the cancer patients, 73% of patients with adenomas, and none of the patients without cancer.

Sharon Olsen, MS, RN, is an investigator on the MACGN grant and Assistant Professor at The Johns Hopkins University School of Nursing.