Colon cancer happens when a group of abnormal cells begins growing in the colon, crowding out the normal cells and forming a malignant tumor. This group of abnormal cells is what we commonly call a “polyp”. A polyp can grow larger and larger over time where it can eventually become cancer. Under the universal title of colorectal cancer, it is often grouped with rectal cancer, which refers to cancer cells that develop in the rectum located at the end of the colon. The National Cancer Institute estimates that there will be 149,500 new cases of colorectal cancer in the US in 2021, making it the fourth most common cancer type. However, colorectal cancer is the second leading cause of cancer death in the US.
The importance of cancer screening
As is the case with most cancers, one of the most important tools available to fight colon cancer is screening. Doctors use regular screenings to check for cancer even before a person has symptoms, which is crucial in successfully treating any tumors that may have formed. Often, by the time a patient presents with cancer symptoms, the cancer may have already begun to spread.
Who Should be Screened?
Previously most cancer prevention groups recommended that people with an average risk of colorectal cancer start regular screening at age 50. However more recently, The American Cancer Society and American College of Gastroenterology, though, changed recommendations that average risk screening should start at age 45. Other organizations have also recently started to slowly amend their guidelines to also lower the recommended age of screening to 45. Bear in mind, that people who have a family history of colorectal cancer or certain conditions such as Lynch syndrome may be advised to start screening even earlier. The USPSTF recommends that screening should continue until at least age 75. Patients over the age of 75 should be discussed on a case-by-case basis based on the patient’s life expectancy and comorbidities.
Types of Colon Cancer Screening
Five different types of tests are used to screen for colorectal cancer. They are fecal occult blood test, DNA stool test, virtual colonoscopy, sigmoidoscopy, and, colonoscopy.
- Colonoscopy: This is the gold standard for colon cancer screening. It requires people to do a preparation to clean out the colon beforehand. The colonoscopy is done by inserting a colonoscope, which, like a sigmoidoscope, is a thin, tube-like instrument with a light and lens for viewing, up through the rectum and into the colon. Once again, similar to the sigmoidoscope, it may also have a tool that can remove tissue samples and polyps, which can be checked under a microscope for signs of cancer.
- Fecal Occult Blood Test: A fecal occult blood test (FOBT) tests a patient’s stool for tiny amounts of blood that can only be seen under a microscope. If your doctor finds blood in your stool, that may indicate the presence of polyps (small clumps of cells that form on the colon wall), cancer, or other conditions. More commonly, bleeding hemorrhoids are a cause of a positive FOBT, however, a bleeding polyp or cancer is still a possibility.
- DNA Stool Test (cologuard): This test is similar to a fecal blood test. However, instead of examining the stool for blood, this will test for genetic changes within the stool that may be a sign of colorectal cancer.
- Virtual Colonoscopy: A less invasive screening method than a sigmoidoscopy or colonoscopy is a virtual colonoscopy. This screening method, also known as computer tomography colonography (CTC), uses CT scans of the colon to create a series of pictures of the colon. When put together, these pictures can produce detailed images that allow your doctor to see if anything abnormal is growing inside the colon. Keep in mind that this still requires people to do a clean out of the colon before the procedure, similar to a colonoscopy.
- Sigmoidoscopy: Alternatively, your doctor may decide to do a sigmoidoscopy, a procedure to examine the rectum and sigmoid (lower) colon for polyps, abnormal areas, or cancer. This is done by inserting a sigmoidoscope, a thin, tube-like instrument with a light and a lens for viewing, through the rectum into the sigmoid colon. The sigmoidoscope may also have a tool that can be used to remove polyps or tissue samples, which will then be checked under a microscope for signs of cancer. It requires only enemas to clean out the lower colon before the test and is often tolerated well awake.
The type of test your doctor may opt for might depend on age, general health, medical history, and non-medical factors such as cost, insurance coverage, and convenience of the test. You should consult with your doctor about which screening test might be best for you.
Risks of Colon Cancer Screening
While colon cancer screening can be an important method of early diagnosis, like many tests, false-negative and false-positive results can occur. This may mean that you either do not get the treatment you need until the cancer has begun developing or that you end up being sent for unnecessary further testing, like biopsies.
There are also specific risks attached to some of the screening methods. These should be discussed with your physician.
The number of colorectal cancer cases has been falling an average of 2% per year over the last ten years, and death rates have fallen by a similar amount. At the same time, the five-year survival rate has risen for patients diagnosed with colorectal cancer. Ensuring that patients continue to be screened for colon cancer, those numbers will hopefully continue to improve.