Cancer of the colon and rectum (also known as colorectal cancer) is the fourth most common cancer in the U.S.--and accounts for about 8 percent of all new cancer cases, according to the National Cancer Institute. The average person has about a one in 20 chance of getting colorectal cancer during his or her lifetime. The five-year survival rate is nearly 70 percent.
Most cases start with the growth of polyps, or clumps of benign cells, that attach themselves to the large intestine. These polyps can become cancerous if they're not caught in time by a colonoscopy (the screening test for colon cancer) and removed.
About 5 to 10 percent of colon cancer cases are caused by an inherited genetic mutation (the rest are known as sporadic). We talked to Dennis J. Ahnen, M.D., professor of medicine at the University of Colorado School of Medicine and the director of the genetics clinic at Gastroenterology of the Rockies, to get his insights into hereditary colon cancer--and the best ways to prevent it if it runs in your family. Here are some need-to-knows:
There are 15 different hereditary colon-cancer syndromes. Two of the most common are Lynch syndrome and familial adenomatous polyposis (FAP). People with FAP develop hundreds of thousands of polyps in the colon and rectum, so the odds of even a few polyps turning cancerous is high.
Each of these inherited syndromes increases your risk of colon cancer, but with different rates. For example, people with Lynch syndrome have a 30 to 60 percent lifetime risk of developing colon or endometrial cancer; people with FAP, nearly 100 percent.
Lynch syndrome also increases your rates for other types of cancer. If Lynch syndrome runs in your family, then you have a 5 to 10 percent increased risk of developing breast, pancreatic, ovarian, gastric, and urinary tract cancers. With FAP, your chances of developing stomach and thyroid cancer go up 5 to 10 percent. Plus, Lynch syndrome can overlap with other genetic mutations, especially BRCA. "About 20 percent of people who get genetic testing because they meet the clinical criteria for Lynch also have a hereditary BRCA mutation for breast and ovarian cancers," says Dr. Ahnen.
Look at your family history If your family meets the 3-2-1 rule then Lynch syndrome may run in your family: Three Lynch syndrome associated cancers--colon, endometrial, ovarian, or pancreatic, say--in your family, involving at least two generations, and one case that occurred to a family member who was younger than 50. Other clues to watch for: were the cancer cases on one side of the family, did someone have multiple cancers that are related (breast and ovarian, or colon and endometrial), or were there multiple cancers in the family.
Tumors can give off clues, too. Doctors can test a tumor for changes in cell DNA known as microsatellite instability. "All of the Lynch cancers show the presence of microsatellite instability," Dr. Ahnen explains. "So there's a growing recommendation that all colon cancers that occur in people younger than 70 be tested for this condition as a way to identify Lynch syndrome families." The best way is to test the youngest Lynch-related cancer patient first. Once doctors find the mutation, they can test other family members to check if they carry the gene as well.
Colonoscopies save lives. Cases of colon cancer are going down--and so is the death rate. This is largely because many more people over 50--the recommended age for people with average risk--are getting screened. But if colon cancer runs in your family, you may have to have a colonoscopy long before you turn 50. That's why it's important to know your family history.
Colon cancer cases are rising for people younger than 50. In fact, it's going up by 1 to 2 percent a year, says Dr. Ahnen. Right now, about 10 percent of all colon cancers occur in younger people; even more worrisome, hereditary cancer syndromes make up a larger percentage of those new cases: 12 percent of those diagnosed between 35 and 50 years old; 18 percent of those people who are younger than 35. Dr. Ahnen's theory: "There's something in the environment that's pushing the risk up--like obesity and inactivity--but we are more than compensating for that by screening the people over 50. But we're not screening those under 50." The takeaway: Start having a conversation with your doctor long before you turn 50 if you suspect the colon cancer in your family is hereditary.
Minimizing the Risk if Colon Cancer Runs In Your Family
Get screened If one of your family members had colon cancer before age 60, or if two members of your family have had colon cancer, you want to start having colonoscopies at age 40 and every five years.
Eat more fruits, vegetables, and whole grains. A high-fiber diet can protect against colon cancer.
Eat less beef and processed meats. They up the risk of colorectal cancer.
Watch your weight--and become more active Obesity can increase your risk for any type of cancer, as can being sedentary.
Talk to your doctor about taking aspirin. A major study found that taking a low-dose aspirin every day can cut the risk of developing colon cancer by nearly 20 percent. "Physical activity and aspirin appears to decrease the development of polyps, decrease the progression of polyps to cancer, and improves outcomes of folks who get cancer," says Dr. Ahnen. But these pain relievers aren't for everyone: You have to be at low risk for developing ulcers and gastric bleeding (all side effects of aspirin use).