Inside your abdominal cavity is the long, tubular digestive tract. The second part of this tube -- the large intestine -- is composed of the colon, which stretches 4 feet to 6 feet, and the rectum, which is only 4 inches to 6 inches long.
The inner lining of this "colorectal tube" can be a fertile breeding ground for small tumors, called polyps (Figure 1). About a quarter of all adults in the U.S. older than age 50 will have at least one colorectal polyp. Most colorectal cancers develop from polyps in glandular tissue of the intestinal lining.
Most polyps are benign, but at least one type is known to be precancerous. These are called adenomatous polyps.
The size of the polyp correlates with the development of Cancer. Polyps less than 1 centimeter in size have a slightly greater than a 1% chance of becoming cancer, but those 2 centimeters or greater have a 40% chance of transforming into cancer. Overall, the incidence is about 5%. Most colorectal cancers develop from polyps in glandular tissue of the intestinal lining.
If colorectal cancer is diagnosed and treated early while the tumor is still localized, the disease is highly curable, with five-year survival rates of about 90%. If the tumor continues to grow, cancer can spread directly through the bowel wall to surrounding lymph nodes, tissues, and organs, as well as into the bloodstream.
Once the cancer spreads to lymph nodes or other organs, successful treatment becomes more difficult. Depending on how advanced the disease is, five-year survival rates range from 9% to 93%.
Cancers of the colon and rectum are the third most common cancer in the U.S., with approximately 150,000 cases diagnosed each year. Like many cancers, colorectal cancer is of particular concern for people older than age 50.
Although diagnosis is often possible at an early stage, many people delay seeking medical care because they are embarrassed or fearful of symptoms related to their bowels. Risk increases significantly after age 50 and continues to increase with age.
What Causes Colorectal Cancer?
The exact cause of colorectal cancer is not known. But there are several risk factors for the disease.
- Other diseases. Colorectal cancer is strongly associated with certain other diseases. Those people considered at high risk include anyone with a personal or family history of colon polyps or colon cancer, inflammatory disease of the colon such as ulcerative colitis or Crohn's disease, and cancers of the pancreas, breast, ovaries, or uterus.
- Heredity. As with any cancer, susceptibility to colorectal cancer is at least partly determined by genetic makeup. A few people inherit medical conditions, such as familial adenomatous polyposis (FAP), MYH-associated polyposis (MAP), Gardner's syndrome, Turcot's syndrome, Peutz-Jagher's syndrome, juvenile polyposis, and Cowden's disease. In all of these disorders, colon polyps develop at an early age and unless treated, these people are almost certain to develop colorectal cancer.
- Hereditary nonpolyposis colon cancer. The disease extends from generation to generation and causes a person to develop colon cancer. This disease is associated with other cancers including endometrial, small bowel, upper urinary tract, bladder, ovary, stomach, bile duct, skin, and some pancreatic cancers. This is also known as the Lynch Syndrome.
- Diet. Diet also contributes to the risk of colorectal cancer, although the cause-and-effect relationship is still unclear. People whose diets are high in fruits and vegetables seem to have a reduced risk. Many studies implicate animal fat and protein as promoters of colorectal cancer, although researchers are cautious about drawing any definite conclusions. Some studies show that regularly eating red meat, which is rich in saturated fat and protein, increases risk, while others find no connection. Some scientists note that fat is the main culprit, while others suspect protein. Others contend that it's not the fat and protein themselves, but the way they are cooked. They note that fats and protein cooked at high temperatures -- especially when broiled and barbecued -- can produce a host of potentially carcinogenic substances linked to colorectal cancer.
- Chemical exposure. Heavy exposure to certain chemicals, including chlorine -- which in small amounts is commonly used to purify drinking water -- may increase the risk of colorectal cancer. Exposure to asbestos is thought to be potentially harmful because it has been implicated in causing formation of polyps in the colon.
- History of certain types of surgery. Surgeries such as ureterosigmoidostomy, which is performed in the treatment of bladder cancer, and a cholecsytecomy (the removal of the gallbladder). Some studies show surgery of the bladder may lead to a risk for colon cancer development, but other studies do not.
- History of colon cancer. A prior case of colon cancer increases the risk of a second colon cancer, especially if the first cancer was diagnosed before the age of 60.
- Smoking and alcohol intake of more than 4 drinks per week increases the risk of developing colon cancer.
- Family history. Those with a first-degree relative with colorectal cancer have an increased risk of the disease. The risk increases if more than one first-degree relative has colon cancer.
- Radiation. Prior radiation increases the risk of cancer to the radiated tissue only.
Understanding Colorectal Cancer
Colorectal Cancer: What Is It?
When doctors find colorectal cancer early, it’s highly curable. It happens when abnormal cells grow in the lining of the large intestine (also called the colon) or rectum. This is a common cancer in both men and women. It has the second highest rate of cancer deaths in the U.S.
What Are Polyps?
Colorectal cancers often start out as polyps -- harmless growths on the inside of the intestines. The two most common types of intestinal polyps are adenomas and hyperplastic polyps. They form when there are problems with the way cells grow and repair the lining of the colon. Most polyps stay harmless, but some can turn cancerous. Removing them early prevents the disease.
Risk Factors You Can't Control
Your risk of colorectal cancer depends on your family history and lifestyle. Things you can't control include:
- Age -- most people with it are older than 50
- Polyps or inflammatory bowel disease
- Family history of colorectal cancer
History of ovarian or breast cancer
Risk Factors You Can Control
You can control some things that raise the risk of colorectal cancer. Try to avoid these:
- Diet high in red or processed meats, or those cooked at high temperatures
- Obesity (having too much fat around the waist)
- Not exercising enough
- Heavy alcohol use
What Are the Symptoms?
Colorectal cancer doesn’t have early warning signs, so it's important to get screened. Finding it early means it's more curable. As the disease gets worse, you may see blood in your stool or have pain in your belly, a change in bowel habits (like constipation or diarrhea), unexplained weight loss, or fatigue. By the time these symptoms appear, tumors tend to be bigger and harder to treat.
Tests that Find Colorectal Cancer
Screening tests are key to finding it early. Starting at age 50, most people should have a colonoscopy every 10 years. This test uses a tube with a tiny camera to look at the whole colon and rectum. It not only finds tumors early, but can also prevent colorectal cancer by removing polyps (shown here).
One type of colonoscopy uses a CT scan to show a 3-D model of your colon. Called virtual colonoscopy, the test can show polyps or other problems without actually placing a camera inside your body. The main disadvantage is that if your doctor finds polyps, you would still need a real colonoscopy to take them out. Your doctor may suggest you have the virtual kind once every 5 years.
Barium enema X-rays allow your doctor a glimpse at the inside of the colon and rectum. It’s another way to find polyps, tumors, or other changes in your intestines. Seen here is an X-ray that shows an "apple core" tumor blocking the colon. Like in a virtual colonoscopy, doctors follow up any abnormalities with a regular colonoscopy. Your doctor may suggest you have a barium enema once every five years.
Instead of a colonoscopy, your doctor may recommend flexible sigmoidoscopy. This test uses a slender tube to look inside your rectum and the bottom part of your colon. The tube has a light and a camera and shows polyps and cancer. If your doctor says this is the right test for you, you should get one every 5 years.
Fecal Blood Tests
The fecal occult blood test and fecal immunochemical test can show whether you have blood in your stool, which can be a sign of cancer. You give samples of your stool to the doctor to study. You may have one of these tests in the years that you don’t have a colonoscopy or sigmoidoscopy. If your doctor says one of the fecal blood tests is right for you, you should take it every year.
An At-Home Choice: DNA Test
A new test called Cologuard looks for blood or suspicious DNA in your stool sample. The test is very accurate at finding colon cancer, but if it does, you still need to follow up with a colonoscopy. Cologuard can’t take the place of a colonoscopy, and it’s so new that the U.S. Preventive Services Task Force doesn’t have guidelines for it yet. A doctor can write a prescription for Cologuard in most U.S. states.
The Right Diagnosis
If a test shows a possible tumor, the next step is a biopsy. During the colonoscopy, your doctor takes out polyps and gets tissue samples from any parts of the colon that look suspicious. Experts study the tissue under a microscope to see whether or not it is cancerous. Shown here is a color-enhanced, magnified view of colon cancer cells.
The Stages of Colorectal Cancer
Experts "stage" any cancers they find -- a process to see how far the cancer has spread. Higher stages mean you have a more serious case of cancer. Tumor size doesn’t always make a difference. Staging also helps your doctor decide what type of treatment you get.
- Stage 0 -- Cancer is only in the innermost lining of the colon or rectum.
- Stage I -- Cancer has grown into the muscle layer of the colon or rectum.
- Stage II -- Cancer has grown into or through the outermost layer of the colon or rectum.
- Stage III -- Cancer has spread to one or more lymph nodes in the area.
- Stage IV -- Cancer has spread to other parts of the body, such as the liver, lung, or bones.
The outlook for your recovery depends on the stage of your cancer. The “5-year survival rate” means the percentage of people who live 5 years or more after being diagnosed. Stage I has a 74% 5-year survival rate, while stage IV has a 5-year survival rate of only 6%.
Can Surgery Help Me?
Surgery has a very high cure rate in the early stages of colorectal cancer. In all but the last stage, doctors remove the tumors and surrounding tissue. If they are big, your doctor may need to take out an entire piece of your colon or rectum. If the cancer affects your liver, lungs, or other organs, surgery probably won’t cure you. But it may help reduce your symptoms.
Fighting Advanced Cancer
Colorectal cancer can still sometimes be cured even if it has spread to your lymph nodes (stage III). Treatment typically involves surgery, radiation (shown here), and chemotherapy. If the cancer comes back or spreads to other organs, it will probably be harder to cure. But radiation and chemotherapy may still reduce symptoms and help you live longer.
Will Chemo Make Me Feel Bad?
Newer chemotherapy drugs are less likely to make you sick. There are also medicines that can help you control your nausea.
Radiofrequency ablation (RFA) uses intense heat to burn away tumors. Guided by a CT scan, a doctor inserts a needle-like device into a tumor and the surrounding area. RFA can destroy some tumors that can’t be surgically removed, like in the liver. Chemotherapy can work with RFA.
Prevent Colorectal Cancer With Diet
You can take steps to dramatically lower your odds of getting colorectal cancer. Eat a nutritious diet, get enough exercise, and control your body fat. Those habits prevent 45% of colorectal cancers. The American Cancer Society recommends a diet heavy on fruits and vegetables, light on processed and red meat, and with whole grains instead of refined grains. That will help you keep a healthy weight.
Prevent Cancer With Exercise
Adults who stay active seem to have a powerful weapon against colorectal cancer. In one study, the most active people were 24% less likely to have the cancer than the least active. It didn't matter whether what they did was work or play. The American Cancer Society recommends exercising 5 or more days a week for at least 30 minutes a day. Vigorous exercise gives you even more benefits in less time -- 20 minutes 3 or 4 days a week.