Signs and symptoms of colon cancer include:
- A change in your bowel habits, including diarrhea or constipation or a change in the consistency of your stool
- Rectal bleeding or blood in your stool
- Persistent abdominal discomfort, such as cramps, gas or pain
- A feeling that your bowel doesn't empty completely
- Weakness or fatigue
- Unexplained weight loss
Many people with colon cancer experience no symptoms in the early stages of the disease. When symptoms appear, they'll likely vary, depending on the cancer's size and location in your large intestine.
When to see a doctor
If you notice any symptoms of colon cancer, such as blood in your stool or a persistent change in bowel habits, make an appointment with your doctor.
Talk to your doctor about when you should begin screening for colon cancer. Guidelines generally recommend colon cancer screenings begin at age 50. Your doctor may recommend more frequent or earlier screening if you have other risk factors, such as a family history of the disease.
In most cases, it's not clear what causes colon cancer. Doctors know that colon cancer occurs when healthy cells in the colon become altered.
Healthy cells grow and divide in an orderly way to keep your body functioning normally. But when a cell is damaged and becomes cancerous, cells continue to divide — even when new cells aren't needed. These cancer cells can invade and destroy normal tissue nearby. And cancerous cells can travel to other parts of the body.
Precancerous growths in the colon
Colon cancer most often begins as clumps of precancerous cells (polyps) on the inside lining of the colon. Polyps can appear mushroom-shaped, or they can be flat or recessed into the wall of the colon. Removing polyps before they become cancerous can prevent colon cancer.
Inherited gene mutations that increase the risk of colon cancer
Inherited gene mutations that increase the risk of colon cancer can be passed through families, but these inherited genes are linked to only a small percentage of colon cancers. Inherited gene mutations don't make cancer inevitable, but they can increase an individual's risk of cancer significantly.
The most common forms of inherited colon cancer syndromes are:
- Familial adenomatous polyposis (FAP). FAP is a rare disorder that causes you to develop thousands of polyps in the lining of your colon and rectum. People with untreated FAP have a greatly increased risk of developing colon cancer before age 40.
- Hereditary nonpolyposis colorectal cancer (HNPCC). HNPCC, also called Lynch syndrome, increases the risk of colon cancer and other cancers. People with HNPCC tend to develop colon cancer before age 50.
FAP, HNPCC and other, rarer inherited colon cancer syndromes can be detected through genetic testing. If you're concerned about your family's history of colon cancer, talk to your doctor about whether your family history suggests you have a risk of these conditions.
Factors that may increase your risk of colon cancer include:
- Older age. The great majority of people diagnosed with colon cancer are older than 50. Colon cancer can occur in younger people, but it occurs much less frequently.
- African-American race. African-Americans have a greater risk of colon cancer than do people of other races.
- A personal history of colorectal cancer or polyps. If you've already had colon cancer or adenomatous polyps, you have a greater risk of colon cancer in the future.
- Inflammatory intestinal conditions. Chronic inflammatory diseases of the colon, such as ulcerative colitis and Crohn's disease, can increase your risk of colon cancer.
- Inherited syndromes that increase colon cancer risk. Genetic syndromes passed through generations of your family can increase your risk of colon cancer. These syndromes include familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer, which is also known as Lynch syndrome.
- Family history of colon cancer and colon polyps. You're more likely to develop colon cancer if you have a parent, sibling or child with the disease. If more than one family member has colon cancer or rectal cancer, your risk is even greater. In some cases, this connection may not be hereditary or genetic. Instead, cancers within the same family may result from shared exposure to an environmental carcinogen or from diet or lifestyle factors.
- Low-fiber, high-fat diet. Colon cancer and rectal cancer may be associated with a diet low in fiber and high in fat and calories. Research in this area has had mixed results. Some studies have found an increased risk of colon cancer in people who eat diets high in red meat.
- A sedentary lifestyle. If you're inactive, you're more likely to develop colon cancer. Getting regular physical activity may reduce your risk of colon cancer.
- Diabetes. People with diabetes and insulin resistance may have an increased risk of colon cancer.
- Obesity. People who are obese have an increased risk of colon cancer and an increased risk of dying of colon cancer when compared with people considered normal weight.
- Smoking. People who smoke cigarettes may have an increased risk of colon cancer.
- Alcohol. Heavy use of alcohol may increase your risk of colon cancer.
- Radiation therapy for cancer. Radiation therapy directed at the abdomen to treat previous cancers may increase the risk of colon cancer.
People with an average risk of colon cancer can consider screening beginning at age 50. But people with an increased risk, such as those with a family history of colon cancer, should consider screening sooner. African-Americans and American Indians may consider beginning colon cancer screening at age 45.
Several screening options exist — each with its own benefits and drawbacks. Talk about your options with your doctor, and together you can decide which tests are appropriate for you.
Make lifestyle changes to reduce your risk
You can take steps to reduce your risk of colon cancer by making changes in your everyday life. Take steps to:
- Eat a variety of fruits, vegetables and whole grains. Fruits, vegetables and whole grains contain vitamins, minerals, fiber and antioxidants, which may play a role in cancer prevention. Choose a variety of fruits and vegetables so that you get an array of vitamins and nutrients.
- Drink alcohol in moderation, if at all. If you choose to drink alcohol, limit the amount of alcohol you drink to no more than one drink a day for women and two for men.
- Stop smoking. Talk to your doctor about ways to quit that may work for you.
- Exercise most days of the week. Try to get at least 30 minutes of exercise on most days. If you've been inactive, start slowly and build up gradually to 30 minutes. Also, talk to your doctor before starting any exercise program.
- Maintain a healthy weight. If you have a healthy weight, work to maintain your weight by combining a healthy diet with daily exercise. If you need to lose weight, ask your doctor about healthy ways to achieve your goal. Aim to lose weight slowly by increasing the amount of exercise you get and reducing the number of calories you eat.
Colon cancer prevention for people with a high risk
Some treatments, including medications and surgery, have been found to reduce the risk of precancerous polyps or colon cancer. However, not enough evidence exists to recommend these medications to people who have an average risk of colon cancer. If you have an increased risk of colon cancer, discuss the benefits and risks of these preventive treatments with your doctor:
- Aspirin. Some evidence links a reduced risk of polyps and colon cancer to regular aspirin use. However, studies of low-dose aspirin or short-term use of aspirin haven't found this to be true. It's likely that you may be able to reduce your risk of colon cancer by taking large doses of aspirin over a long period of time. But using aspirin in this way carries a risk of side effects, such as gastrointestinal bleeding and ulcers.
- Celecoxib (Celebrex). Celecoxib and other drugs known as COX-2 inhibitors provide pain relief. Some evidence suggests COX-2 drugs can reduce the risk of precancerous polyps in people who've been diagnosed with these polyps in the past. But COX-2 drugs carry a risk of heart problems, including heart attack. Two COX-2 inhibitor drugs were removed from the market because of these risks.
- Surgery to prevent cancer. In cases of rare, inherited syndromes such as familial adenomatous polyposis, or inflammatory bowel disease such as ulcerative colitis, your doctor may recommend removal of your entire colon and rectum in order to prevent cancer from occurring.