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 done 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 147,950 people in the United States develop colorectal cancer and about 53,200 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.
Risk Factors of Colorectal Cancer
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 (hereditary nonpolyposis colorectal carcinoma [HNPCC])
Lynch syndrome comes from an inherited gene mutation that causes colorectal 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 and cancer of the small intestine, bile ducts, kidneys, and ureters.
MUTYH polyposis syndrome
MUTYH polyposis syndrome is a rare genetic disorder that is an uncommon cause of colorectal cancer. It is due to genetic mutations of the MUTYH gene. More than half of the people who have this syndrome develop colorectal cancer starting in their 60s. They are also at increased risk of developing other types of cancer, such as other digestive tract and bone cancers, and also cancer of the ovaries, bladder, thyroid, and skin.
Symptoms of Colorectal 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.
Diagnosis of Colorectal Cancer
Colonoscopy
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.
Diagnostic tests
Colonoscopy
CT scan if cancer is found
Genetic testing for Lynch syndrome
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.
Lab Test
CEA Test
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.
Diagnosis of MUTYH polyposis syndrome is established by genetic testing.
Screening tests
Colonoscopy
Stool tests
Sigmoidoscopy
Computed tomography (CT) colonography
Fecal testing for blood and cancer DNA
Early diagnosis depends on routine screening, which should typically begin at age 45 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.
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.
