Colorectal Cancer

Risk Factors

The American Cancer Society defines a risk factor as anything that increases a person's chance of getting a disease such as cancer. According to ACS, different cancers have different risk factors. For example, unprotected exposure to strong sunlight is a risk factor for skin cancer, and smoking is a risk factor for lung cancer. According to the American Cancer Society, the following are risk factors for colon and rectum cancer:

A family history of colorectal cancer: If you have a first-degree relative (parent, sibling, or offspring) who has had colorectal cancer your risk for developing this disease is increased. The risk increases even further if the relative is affected before the age of 60, or if more than one relative is affected (at any age). About 5% of patients with colorectal cancer have an inherited genetic abnormality that causes the cancer. One abnormality is called familial adenomatous polyposis (FAP) and a second is called hereditary nonpolyposis colorectal cancer (HNPCC). These abnormalities are described further on in this document. No other clearly identified genetic abnormalities have been described.

Most families with colorectal cancer do not have one of these known genetic syndromes. Accurate identification of people with these syndromes is important. Then doctors can recommend specific measures such as screening at an early age. This will help catch it early and may even block the cancer from developing because polyps may be found before they change into cancer. People with a family history suggesting a colorectal cancer syndrome should consider genetic counseling. This will help them decide about getting screened at an early age.

The American Cancer Society and several other medical organizations recommend earlier screening for people with increased colorectal cancer risk that differ from those generally recommended for people at average risk. For more information, speak with your doctor and/or refer to the table in the "Can Colorectal Cancer Be Found Early?" section of this document.

Familial colorectal cancer syndromes
Familial adenomatous polyposis is a disease where people typically develop hundreds of polyps in their colon and rectum. Usually this occurs between the ages of 5 and 40. Cancer usually develops in one or more of these polyps beginning at age 20, affecting nearly all people with this disorder by age 40, if preventive surgery is not done. Familial adenomatous polyposis is sometimes associated with Gardner's syndrome, a condition that has benign (not cancerous) tumors of the skin, soft connective tissue, and bones. About 1% of all colorectal cancers are due to this syndrome.

Hereditary nonpolyposis colon cancer is the other clearly defined genetic syndrome. It accounts for 3% to 4% of all colorectal cancers. This also develops when people are relatively young. These people also have polyps, but they only have a few, not hundreds. Women with this condition also have a very high risk of developing cancer of the endometrium (lining of the upper part of the uterus).

Doctors have found that families with this syndrome have certain characteristics: 1) at least 3 relatives have colorectal cancer, 2) two successive generations are involved, 3) one of these had cancer when younger than 50, and 4) at least two of the people are first-degree relatives. If this is true of your family, then you might want to seek genetic counseling.

Doctors are also suspicious of this syndrome if, instead of colorectal cancer the family members have other cancers associated with this gene mutation. These are endometrial cancers, ovarian cancers, small bowel cancers, or cancer of the lining of the kidney or the ureter. Still, one member under age 50 must have been diagnosed with colorectal cancer.

Ethnic background: Jews of Eastern European descent (Ashkenazi Jews) are thought to have a higher rate of colorectal cancer. Recent research has found a genetic mutation leading to colorectal cancer in this group. This DNA change occurs much more commonly than the 3 other colorectal cancer syndromes and is present in about 6% of American Jews. In one study, about 10% of colorectal cancers in Jews of Eastern European descent were associated with this mutation. This gene change is called the I1307K APC mutation. It isn't clear though that this genetic change is responsible for the increased number of colorectal cancers in Ashkenazi Jews.

A personal history of colorectal cancer: If you have had colorectal cancer, even though it has been completely removed, you are more likely to develop new cancers in other areas of the colon and rectum. The chances of this happening are much greater if you had your first colorectal cancer when you were age 60 or younger.

A personal history of intestinal polyps: Some types of polyps (inflammatory polyps) do not increase the risk of colorectal cancer. Other types, such as adenomatous polyps and perhaps hyperplastic polyps in the ascending colon, do increase the risk of colorectal cancer. This is especially true if the polyps are large or there are many of them.

A personal history of chronic inflammatory bowel disease: Chronic inflammatory bowel disease (ulcerative colitis) is a condition in which the colon is inflamed over a long period of time. If you have chronic inflammatory bowel disease, your risk of developing colon cancer is increased. You should start being screened at a young age, and the procedure should be repeated frequently. Often the first sign that cancer may be developing is called dysplasia. Dysplasia means the cells lining your colon or rectum look as if they will turn into cancer.

Aging: Your chances of developing colorectal cancer increase markedly after age 50. About 90% of people found to have colorectal cancer are older than 50.

A diet mostly from animal sources: A diet mostly of foods that are high in fat, especially from animal sources, can increase your risk of colorectal cancer. Instead, the American Cancer Society recommends choosing most of your foods from plant sources and limiting your intake of high-fat foods such as those from animal sources. The ACS also recommends eating at least 5 servings of fruits and vegetables every day and several servings of other foods from plant sources such as breads, cereals, grain products, rice, pasta, or beans. Many fruits and vegetables contain substances that interfere with the process of cancer formation.

Physical inactivity: If you are not physically active, you have an increased risk of developing colorectal cancer.

Obesity: If you are very overweight, your risk of developing colorectal cancer is increased. This is particularly true if you are fatter in your waist area than in your thighs or hips. Researchers suggest that the excess fat changes metabolism in a way that increases growth of cells in the colon and rectum, and that fat cells in the waist area have the largest impact on metabolism.

Diabetes: People with diabetes have a 30%-40% increased chance of developing colon cancer. They also tend to have a higher death rate after diagnosis.

Smoking: Recent studies indicate that smokers are 30% to 40% more likely than nonsmokers to die from colorectal cancer. Smoking may be responsible for causing about 12% of fatal colorectal cancers. Almost everyone knows that smoking causes cancers in sites in the body that come in direct contact with the smoke, such as the mouth, larynx, and lungs. However, some of the cancer-causing substances are swallowed and can cause digestive system cancers, such as esophageal and colorectal cancer. Some of these substances are also absorbed into the bloodstream and can increase the risk of developing cancers of the kidneys, bladder, cervix, and other organs.

Alcohol intake: Colorectal cancer has been linked to the heavy use of alcohol. While some of this may be due to the effects of alcohol on folic acid in the body, it still would be wise to avoid heavy alcohol use.

Support & Information

Colo-Rectal Cancer Network
Offers support for the family/friends of colorectal cancer patients.

National Colorectal Cancer Research Alliance
Information on colorectal cancer and preventive testing.

Colon Cancer Alliance
Basic information about colorectal cancer, survivor stories and personal stories.

The American Society of Colon and Rectal Surgeons
A site dedicated primarily to facilitating searches for colorectal surgeons in your area.

National Colorectal Cancer Awareness Month
Gives patients and their families information, materials, recent news and updates, as well as events.

Minnesota Colorectal Cancer Consortium
Increases public awareness about colorectal cancer, encourages correct screening, provides information on available treatments and support groups for patients and their families and friends. Also includes an online quiz about colorectal cancer.