Colorectal cancer is the third leading cause of cancer deaths among American men and women. These cancers arise from the inner lining of the large intestine, also known as the colon. Tumors may also arise from the inner lining of the very last part of the digestive tract, called the rectum.
Unfortunately, most colorectal cancers are "silent" tumors. They grow slowly and often do not produce symptoms until they reach a large size. Fortunately, colorectal cancer is preventable, and curable, if detected early.
How Does Colorectal Cancer Develop?
Colorectal cancer usually begins as a "polyp," a nonspecific term to describe a growth on the inner surface of the colon. Polyps are often non-cancerous growths, but some can develop into cancer.
The two most common types of polyps found in the colon and rectum include:
- Hyperplastic and inflammatory polyps. Usually these polyps do not carry a risk of developing into cancer. However, large hyperplastic polyps, especially on the right side of the colon, are of concern and should be completely removed.
- Adenomas or adenomatous polyps. Polyps, which, if left alone, could turn into colon cancer. These are considered pre-cancerous.
Although most colorectal polyps do not become cancer, virtually all colon and rectal cancers start from these growths. People may inherit diseases in which the risk of colon polyps and cancer is very high.
Colorectal cancer may also develop from areas of abnormal cells in the lining of the colon or rectum. This area of abnormal cells is called dysplasia and is more commonly seen in people with certain inflammatory diseases of the bowel such as Crohn's disease or ulcerative colitis.
What Are the Risk Factors for Colorectal Cancer?
While anyone can get colorectal cancer, it is most common among people over age 50. Risk factors for colorectal cancer include:
- A personal or family history of colorectal cancer or polyps
- A diet high in red meats and processed meats
- Inflammatory bowel disease (Crohn's disease or ulcerative colitis)
- Inherited conditions such as familial adenomatous polyposis and hereditary non-polyposis colon cancer
- Physical inactivity
- Heavy alcohol use
- Type 2 diabetes
- Being African-American
What Are the Symptoms of Colorectal Cancer?
Unfortunately, colorectal cancer may strike without symptoms. For this reason, it is very important to talk to your doctor about whether you are at risk for colorectal cancer and should be screened.
In addition to getting a medical history and physical exam, there are a number of tests your doctor can perform to help detect colorectal cancer and polyps early. Tests to help detect colorectal polyps and cancer include:
- Sigmoidoscopy. This is a procedure used to examine the rectum and very last part of the colon. This test can detect polyps, cancer, and other abnormalities in the sigmoid colon and rectum. During this exam, a biopsy (tissue sample) may also be removed and sent for testing.
- Stool DNA. A stool DNA test looks for changes in genes that are sometimes found in colon cancer cells. This test can find some colon cancers before symptoms develop.
- Colonoscopy. A colonoscopy examines the entire colon and rectum. During this procedure, polyps can be removed and sent for testing.
- CT colonography. This is a special X-ray test (also referred to as a virtual colonoscopy) done of the entire colon using a CT (computed tomography) scanner. This test takes less time and is less invasive than other tests. However, if a polyp is detected, a standard colonoscopy needs to be performed.
The earliest sign of colon cancer may be bleeding. Often tumors bleed only small amounts intermittently, and evidence of the blood is found only during chemical testing of the stool. This is called occult bleeding, meaning it is not always visible to the naked eye. When tumors have grown to a large size they may cause a change in the frequency or the caliber of the stool. The two following tests look for hidden blood in the stool:
- Fecal immunochemical test (FIT). The FIT reacts to part of the human hemoglobin protein, which is found in red blood cells. It can be performed at home, with a test kit that includes a mailing envelope with which to send the stool sample to a lab.
- Guaiac-based fecal occult blood tests (gFOBT).This test also looks for blood in your stool. It can also be done at home.
If either of these tests have a positive result, your doctor will likely recommend a colonoscopy to investigate further.
Symptoms of colorectal cancer include:
- A persistent change in bowel habits (such as constipation or diarrhea)
- Blood on or in the stool
- Abdominal discomfort
- Unexplained weight loss
What Happens If a Colorectal Polyp Is Found?
If colorectal polyps are found, they should be removed and sent to a laboratory for microscopic analysis. Once the microscopic type of polyp is determined, the follow-up interval for the next colonoscopy can be made.
How Is Colorectal Cancer Treated?
The majority of colorectal polyps can be removed during a routine colonoscopy and examined under a microscope. Very large adenomas and cancers are removed with surgery. If the cancer is found in the early stages, surgery can cure the disease. Advanced colorectal cancers may be treated in a variety of ways, depending on their location. Treatments include surgery, radiation therapy, chemotherapy, and targeted therapy.
How Can I Prevent Colorectal Cancer?
Living a healthy lifestyle that includes no smoking, regular exercise, maintenance of a healthy weight, and a diet that is low in red meat and high in vegetables and fruit is probably your best start at general cancer prevention.
Some studies have shown that aspirin and other drugs known as nonsteroidal anti-inflammatory drugs, or NSAIDs, may help prevent colon cancers. NSAIDs also carry increased risks of serious complications, such as stomach bleeding, heart attacks and strokes. Low dose aspirin is sometimes recommended for prevention of colon cancer in adults ages 50 to 69. Talk with your doctor before taking aspirin for this purpose.
Screening for cancer is another important step.
General Colorectal Cancer Screening Recommendations:
These recommendations are for people at average risk for colorectal cancer without symptoms or a personal or family history of colorectal polyps or cancer or inflammatory bowel disease. Screening should begin at age 50.
Stool tests – a fecal occult blood test or fecal immunochemical test -- is performed once a year. These are simple at-home tests that check for hidden blood in the stool from multiple samples. A stool DNA test every 3 years looks for changes in DNA that may indicate colon polyps or cancer. A colonoscopy should be done if stool test results are abnormal.
- Flexible sigmoidoscopyperformed every 5 years. This is an outpatient procedure for examining the inside of the lower portion of the large intestine, called the sigmoid colon, and also the rectum. This test can miss polyps, cancer, or other abnormalities that are beyond the reach of the scope. If abnormalities are detected, a colonoscopy needs to be done.
- Colonoscopy, performed once every 10 years; this is the preferred test.
- CT colongraphy (virtual colonoscopy) performed every 5 years. This can miss small polyps. If any abnormalities are detected, a colonoscopy is needed.
People at higher risk for colorectal cancer include those with a personal history of polyps on previous colonoscopy, colorectal cancer, and/or inflammatory bowel disease, strong family history of colorectal cancer or precancerous polyps, and a family history of a hereditary cancer syndrome. Screening guidelines for adults consist of screening with colonoscopy starting at a younger age. However, the exact age to start screening and interval of testing depends on specific risk factors.