Family history and some dietary factors (low fiber, high fat) increase a person’s risk of colorectal cancer.
Typical symptoms include bleeding during a bowel movement, fatigue, and weakness.
Screening tests are important for people over 50.
Colonoscopy is often used to make the diagnosis.
Cancer that is caught early is most curable.
Surgery is usually performed to remove the cancer.
Almost all cancers of the large intestine and rectum (colorectal) are adenocarcinomas, which develop from the lining of the large intestine (colon) and rectum. Colorectal cancer usually begins as a buttonlike growth on the surface of the intestinal or rectal lining called a polyp. As the cancer grows, it begins to invade the wall of the intestine or rectum. Nearby lymph nodes also may be invaded. Because blood from the wall of the intestine and much of the rectum is carried to the liver, colorectal cancer can spread (metastasize) to the liver after spreading to nearby lymph nodes.
In Western countries, cancer of the large intestine and rectum is one of the most common types of cancer and the second leading cause of cancer death. The incidence of colorectal cancer begins to rise sharply around age 40 to 50. Each year, about 135,000 people in the United States develop colorectal cancer and about 50,000 die.
Colorectal cancer is slightly more common among men than women. About 5% of people with colon cancer or rectal cancer have cancer in two or more sites in the colon and rectum that do not seem to simply have spread from one site to another.
People with a family history of colorectal cancer have a higher risk of developing the cancer themselves. A family history of intestinal adenomatous polyps also increases the risk of colorectal cancer.
People with ulcerative colitis or Crohn disease of the colon are at greater risk as well. This risk is related to the person’s age when the disease developed, the amount of intestine or rectum that is affected, and the length of time the person has had the disease.
People at highest risk tend to consume a diet that is high in fat, animal protein, and refined carbohydrates and low in fiber. Greater exposure to air and water pollution, particularly to industrial cancer-causing substances (carcinogens), may play a role.
Lynch syndrome comes from an inherited gene mutation that causes cancer in 70 to 80% of the people with that mutation. People with Lynch syndrome often develop colorectal cancer before age 50. They are also at increased risk of other types of cancer, particularly endometrial cancer and ovarian cancer, but also stomach cancer, cancer of the small intestine, and kidney cancer.
Colorectal cancer grows slowly and does not cause symptoms for a long time. Symptoms depend on the type, location, and extent of the cancer.
Fatigue and weakness resulting from occult bleeding (bleeding not visible to the naked eye) may be the person’s only symptoms.
A tumor in the left (descending) colon is likely to cause obstruction at an earlier stage, because the left colon has a smaller diameter and the stool is semisolid. The person may seek medical treatment because of crampy abdominal pain or severe abdominal pain and constipation.
A tumor in the right (ascending) colon does not cause obstruction until later in the course of the cancer, because the ascending colon has a large diameter and the contents flowing through it are liquid. By the time the tumor is discovered, therefore, it may be larger than a tumor on the left.
Most colon cancers bleed, usually slowly. The stool may be streaked or mixed with blood, but often the blood cannot be seen. The most common first symptom of rectal cancer is bleeding during a bowel movement. Whenever the rectum bleeds, even if the person is known to have hemorrhoids or diverticular disease, doctors must consider cancer as a possible diagnosis. Painful bowel movements and a feeling that the rectum has not been completely emptied are other symptoms of rectal cancer. Sitting may be painful, but otherwise the person usually feels no pain from the cancer itself unless it spreads to tissue outside the rectum.
People who have symptoms that suggest colon cancer or who have a positive screening test need a diagnostic test to confirm whether they do or do not have cancer.
Screening tests for colon cancer are tests done to detect cancer in people who do not have symptoms of cancer but are at risk of cancer.
People with blood in their stool require colonoscopy, as do those with abnormalities seen during a sigmoidoscopy or an imaging study. Any growths or abnormalities seen should be completely removed during the colonoscopy.
Barium enema x-rays may be taken to detect tumors in the lower part of the large intestine. However, colonoscopy is the preferred diagnostic test because during colonoscopy doctors can take tissue samples to see whether a growth is cancerous or not.
Once cancer is diagnosed, doctors usually do an abdominal CT scan, chest x-ray, and routine laboratory tests to look for cancer that has spread, to detect a low blood count (anemia), and to evaluate the person’s overall condition.
Blood tests are not used to diagnose colorectal cancer, but they can help the doctor monitor the effectiveness of treatment after a tumor has been removed. For example, if levels of the cancer marker carcinoembryonic antigen (CEA) are high before surgery to remove a known cancer but are low after surgery, monitoring for another increase in the CEA level may help detect an early recurrence of the cancer. Two other cancer markers, CA 19-9 and CA 125, are similar to CEA and are sometimes elevated in colorectal cancer.
Colon cancers that were removed during surgery are now routinely tested for the gene mutations that cause Lynch syndrome. People with relatives who developed colon, ovarian, or endometrial cancer at a young age or who have multiple relatives with those cancers should be tested for Lynch syndrome.
Early diagnosis depends on routine screening, which should typically begin at age 50 for people who are at average risk of developing colorectal cancer and continue until age 75. For adults aged 76 to 85, doctors take into consideration the person's overall health and the results of previous screenings and then decide whether to continue screening. Screening begins earlier in some people. For example, people who have a first-degree relative (a parent, sibling, or child) who has had colorectal cancer before age 60 should begin screening every 5 years beginning at age 40 or 10 years earlier than the age of diagnosis of the relative, whichever is sooner. For example, if a person's father was diagnosed with colorectal cancer at age 45, he or she should begin screening at age 35. Also, some authorities suggest that for blacks, screening should begin at age 45.
Doctors often screen people using colonoscopy, in which the entire large intestine is examined. With colonoscopy, the test needs to be done only every 10 years. During colonoscopy, growths that appear cancerous (malignant) are removed using instruments passed through the scope. Growths are sent to the laboratory to be tested for cancer. Some larger growths must be removed during regular surgery.
Blood in the stool, even blood that cannot be seen by the naked eye (occult blood—see Stool Occult Blood Tests), can be a sign of cancer. Usually, the stool is tested every year. To help ensure accurate test results, the person eats a high-fiber diet that is free of red meat for 3 days before providing a stool sample. Newer stool tests for occult blood (immunochemical tests) are more accurate than older stool tests and have no dietary restrictions. However, many disorders besides cancer can cause blood in the stool and not all cancers bleed at all times. Some new stool tests look for genetic material from a cancer rather than for blood. Genetic stool tests are done every 3 years.
Sigmoidoscopy (examination of the lower portion of the large intestine with a viewing tube—see Endoscopy) is another diagnostic procedure used for screening. Sigmoidoscopy is good for lesions in the sigmoid colon or rectum but does not reveal tumors further up in the colon. Sigmoidoscopy needs to be done every 5 years or, if occult blood testing is also done, every 10 years.
CT colonography (virtual colonoscopy) generates three-dimensional images of the colon by using a special CT scan technique. In this technique, people drink a contrast agent and their colon is inflated with gas from a tube inserted in the rectum. Viewing the high-resolution three-dimensional images somewhat simulates the appearance of regular endoscopy, hence the name. Virtual colonoscopy may be an option for people who are unable or unwilling to undergo the regular colonoscopy procedure, but it is less accurate and highly dependent on the skill and experience of the radiologist. Virtual colonoscopy does not require sedation but still requires a thorough bowel preparation, and the inflation of the colon with gas may be uncomfortable. Additionally, unlike with regular colonoscopy, lesions cannot be removed for examination under a microscope (biopsied) during the procedure. Virtual colonoscopy can show whether cancer has spread outside of the colon to the lymph nodes or liver but is not good for detecting small polyps in the colon. This test is done every 5 years.
People with Lynch syndrome require ongoing screening for other cancers. Such screening includes ultrasonography of the female organs (done through the vagina), examination of cells taken from the lining of the uterus (endometrium) with a suction device, and tests of the blood and urine. Close family members of people with HNPCC should have colonoscopy every 1 to 2 years beginning in their 20s, and women should be tested every year for endometrial and ovarian cancer.
Colon cancer is most likely to be cured if it is removed early, before it has spread. Cancers that have grown deeply or through the wall of the colon have often spread, and sometimes these cancers cannot be detected. The 10-year survival rate is about 90% when the cancer is only in the lining of the bowel wall, about 70 to 80% when the cancer extends through the bowel wall, only about 30 to 50% when the cancer has spread to the lymph nodes in the abdomen, and less than 20% when the cancer has metastasized to other organs.
In most cases of colon cancer, the cancerous segment of the intestine and any nearby lymph nodes are removed surgically, and the remaining ends of the intestine are joined. If the cancer has penetrated the wall of the large intestine and spread to a very limited number of nearby lymph nodes, chemotherapy after surgical removal of all visible cancer may lengthen survival time, although the effects of these treatments are often modest.
For rectal cancer, the type of operation depends on how far the cancer is located from the anus and how deeply it has grown into the rectal wall. The complete removal of the rectum and anus means the person needs a permanent colostomy. A colostomy is a surgically created opening between the large intestine and the abdominal wall. The contents of the large intestine empty through the abdominal wall into a colostomy bag. If doctors can leave part of the rectum and the anus is intact, the colostomy may be temporary. After these tissues have had time to heal (over several months), another surgery can be done to rejoin the rectal stump to the end of the large intestine, and the colostomy can be closed.
When rectal cancer has penetrated the rectal wall and spread to a very limited number of nearby lymph nodes, giving chemotherapy plus radiation therapy (see Combination Cancer Therapy) after surgical removal of all visible cancer may lengthen survival time. Some doctors give chemotherapy and radiation therapy before surgery.
When cancer has spread to lymph nodes far from the colon or rectum, to the lining of the abdominal cavity, or to other organs, the cancer cannot be cured by surgery alone. However, surgery is sometimes done to relieve any intestinal obstruction and ease symptoms. Chemotherapy with a single drug or combination of drugs may shrink the cancer and prolong life for several months. The doctor usually discusses end-of-life care with the person, the family, and other health care practitioners (see Treatment Options at the End of Life).
Staging Colon Cancer
When the cancer has spread only to the liver and there are 3 or fewer tumors (metastases), doctors sometimes remove these tumors surgically. Alternatively, doctors may inject chemotherapy drugs or radioactive beads directly into the artery supplying the liver with blood. A small pump inserted surgically beneath the skin or an external pump worn on a belt allows the person to be mobile during the treatment. This treatment may provide more benefit than ordinary chemotherapy, but more research is needed. When cancer has spread beyond the liver, this approach has no advantage.
If the cancer is obstructing the colon in a person who cannot tolerate surgery because of poor health, doctors may try to relieve symptoms in other ways. One treatment involves shrinking the tumor with a probe that applies an electric current (electrocautery) or sometimes with a laser. Alternatively, doctors may use an expandable wire mesh tube (stent) to hold the obstructed area open. All of these treatments can be done through a colonoscope. Although the person often feels better for a while, these treatments do not lengthen survival time.
After surgery, colonoscopy should be done within 1 year. A second colonoscopy should be done 3 years after that if no polyps or tumors are found. Thereafter, colonoscopy should be done every 5 years.
Doctors also do a physical examination and blood tests such as a complete blood count and liver function tests at regular intervals after surgery. Imaging tests such as CT or MRI are also performed on a regular schedule.