Top 5 Things to Know About Colorectal Cancer Screening

By Walter Coyle, MD, Gastroenterologist

By Walter Coyle, MD, Gastroenterologist

It’s not something most people want to talk about, but by age 50, you should have a conversation with your doctor about colorectal cancer.

Here’s what you need to know about this serious, but often preventable, disease.

1. Colorectal cancer is the third most common cancer diagnosed in the United States and the second leading cause of cancer death.

This is true for both men and women. Colorectal cancer will affect about one in 20 people. Women have a slightly lower risk than men of developing the disease. The American Cancer Society estimates that 95,270 new cases of colon cancer and 39,220 new cases of rectal cancer will be diagnosed in the U.S. this year.

2. Colorectal cancer develops slowly, with few early signs or symptoms.

Colorectal cancer almost always starts with an abnormal growth known as a polyp in the colon or rectum. Not all polyps are malignant, but those that are tend to grow slowly, often taking 10 years to become cancerous. This is why there are generally few symptoms during the early stages of the disease.


As it progresses, symptoms may include blood in the stool, rectal bleeding, abdominal pain, or a change in bowel habits that lasts for a few days or more, such as diarrhea, constipation, or narrowing of the stool. If you notice any of these symptoms, call your doctor. Other conditions may also cause these symptoms, so it is important to identify the cause and get treatment.

3. Screening prevents most colorectal cancer.

Because polyps in the colon or rectum grow so slowly, the goal is to find and remove them before they become cancerous. There are several types of colorectal screening tests. Some only detect potentially cancerous growths, while others detect and remove them.


A colonoscopy is considered the “gold standard” of colorectal cancer screening. The procedure is performed while you are sedated, so you do not feel or see anything. The doctor inserts a flexible tube with a small camera into the rectum to examine the entire length of the colon. If precancerous polyps are found, they often can be removed during the procedure.


Flexible sigmoidoscopy is a similar procedure that uses a shorter tube to view only the lower third of the colon. Medicare and most insurance companies cover these tests for people 50 and older.


Because the colon needs to be empty for these procedures, you must drink only clear liquids for 24 hours and take a special prescription laxative to clear your colon.


A FIT, or fecal immunochemical test, analyzes a stool sample for signs of blood from cancer. No prep is necessary. However, this test is not as thorough as a colon exam, and if cancer is suspected or the FIT test is positive, a colonoscopy may be needed. Usually the FIT test is performed every year.


Stool DNA testing has received a lot of media coverage recently and is now covered by Medicare. This test is better than the FIT stool test for detecting colon cancer and some large polyps and does not require prep. But it is expensive and is falsely positive about 10 percent of the time. Further study is required to determine how we are going to use it in clinical practice. Current recommendations are to repeat stool DNA testing every three years.


Some tests, such as a virtual or CT colonoscopy, currently are not covered by Medicare or most insurance health plans. The colon capsule is also under study and is only approved by Medicare for those patients who fail colonoscopy.

4. Everyone should be screened by age 50 – or earlier.

An initial colonoscopy screening is recommended for everyone at age 50. About nine out of 10 people diagnosed with colorectal cancer are at least 50 years old. If you have a family history of colorectal cancer or risk factors such as inflammatory bowel disease, your doctor may recommend having your first screening at a younger age.


For African-Americans, there is about a 20 percent higher risk for colorectal cancer. The American College of Gastroenterology (ACG) recommends a first screening at age 45 for this population.


For most people, colonoscopy screenings should be repeated every 10 years.

5. A colonoscopy can save your life.

Unfortunately, only about 60 percent of people in the U.S. who should be screened for colorectal cancer actually have the test. Many may be put off by the preparation required. However, it is a small price to pay for a procedure that can be life-saving. According to the ACG, cancer risk is reduced by 90 percent following a colonoscopy and the removal of precancerous polyps.


In addition, a national study recently published in the New England Journal of Medicine found a 53 percent lower death rate from colorectal cancer among people who had a colonoscopy and a precancerous polyp removed, compared to the general population. Many patients were followed for 20 years.


Talk to your doctor about when and how you should be screened for colon cancer.