4 Things to Know About Colorectal Cancer Screenings

Learn how screening is done and why it is so important

Scripps Health in San Diego provides preventive screenings for colorectal cancer.

Colorectal cancer is one of the most common types of cancer. It will affect one in 20 people in the United States this year, and it is the third most common cancer diagnosed among both men and women. Fortunately, this is also one of the most preventable types of cancer.


“The good news is that screening for colorectal cancer can help catch potential cancers before they develop,” says Walter Coyle, MD, a gastroenterologist at Scripps Clinic, Torrey Pines.

Frequently asked questions about colorectal cancer screenings

Dr. Coyle notes that there are four main things that patients ask him about screenings for colon and rectal cancers.


1. Why is screening for colorectal cancer so important?
“Colorectal cancer almost always begins with an abnormal growth called a polyp in the colon or rectum,” says Dr. Coyle. “Polyps develop slowly and can take 10 years to become cancerous. If we find them early, we can remove them before they turn into cancer.”
According to the American College of Gastroenterology, the risk for colon cancer is reduced by 90 percent following a colonoscopy and the removal of precancerous polyps.


Screening is especially valuable because the disease has few symptoms in its early stages, adds Dr. Coyle. By the time symptoms such as blood in the stool or a change in bowel habits occur, the cancer may have already progressed. If you do notice these symptoms, call your doctor.


2. How is colorectal cancer screening done?
There are several types of screening exams for colorectal cancer. A colonoscopy is the most common and thorough screening because it enables the physician to examine the entire length of the colon. While the patient is sedated, a flexible tube with a small camera is inserted into the rectum and moved along the colon. If precancerous polyps are found, they can often be removed during the procedure.


A similar procedure, flexible sigmoidoscopy, uses a shorter tube to view only the lower third of the colon.


Less invasive tests include a FIT test, or fecal immunochemical test, which analyzes a stool sample for signs of cancer. However, this test is not as thorough as a colon examination, and if cancer is suspected, a colonoscopy may still be needed.


Another type of stool screening, stool DNA testing, is now covered by Medicare. “This test is better than the FIT stool test for detecting colon cancer, but it is expensive and is falsely positive 10 percent of the time,” says Dr. Coyle. “Further study is required to determine how we are going to use it in clinical practice.”


3. What do I need to do to prepare for the screening?
Both a colonoscopy and a flexible sigmoidoscopy require a preparation process to ensure that the colon is completely empty. You need to drink large amounts of clear liquids, including laxatives, over a 24-hour period prior to the exam. It is critical to follow the preparation process; if your colon is not completely empty, the test cannot be done.


“Some people find the prep uncomfortable, but don’t skip the screening because you don’t want to do the prep,” says Dr. Coyle. “These preventive exams can save your life.” If you are really concerned, talk to your doctor.


4. When should people be screened?
“Most people should have their first colonoscopy at age 50,” says Dr. Coyle. “But if you have risk factors such as a family history of colorectal cancer, or you have inflammatory bowel disease, your doctor may recommend that your first screening be done sooner.”


Dr. Coyle adds that African-Americans, who have a 20 percent greater risk of colorectal cancer, should get a screening beginning at age 45.


In general, colonoscopy screenings should be repeated every 10 years. “Your individual health history determines the right screening schedule for you,” says Dr. Coyle. “Ask your doctor when you should start screening and how often to have follow-up exams.”