Colorectal cancer screening: What are the options?

March 08, 2021
Dr. Thomas Curran stands outside
With colorectal cancers on the rise in younger populations, Dr. Thomas Curran encourages patients to get screened based on the latest guidelines. Photo by Marquel Coaxum

Colorectal cancer is common in the United States, affecting about one in 23 men and one in 25 women. While the rate of colon and rectal cancer diagnoses has dropped overall since the mid-1980s, this trend is mostly due to a decrease in incidence among older adults, masking a rising incidence among younger populations.

According to Thomas Curran, M.D., a surgeon in MUSC’s Division of Colon and Rectal Surgery who practices at MUSC Hollings Cancer Center, one in every three new rectal cancers is diagnosed in patients younger than 55, making it incredibly important that patients don't delay in getting their first screening.

Because of this upward trend, the American Cancer Society recently changed its recommendation for average-risk patients to begin screening at age 45 instead of 50. But knowing what type of screening to get and how often can be confusing.

In honor of Colorectal Cancer Awareness Month, Curran discussed the various screening options for colorectal cancer and what you need to know about their frequency and reliability.

What types of screening tests exist, and what are the pros and cons of each?

Screening for colorectal cancer can be done in three ways:

  1. Stool-based testing.
  2. Endoscopic testing (i.e. a colonoscopy).
  3. CT colonography, which is a special CAT scan that looks closely at the lining of the colon.

The major benefit of stool-based testing is that it can generally be done at home, and it does not require a bowel prep or a large dose of laxatives to clean out the colon. Both colonoscopies and CT colonographies require a bowel prep.

However, only colonoscopies are diagnostic as well as therapeutic, meaning that if stool-based testing or a CT colonography comes back positive, then a colonoscopy will be recommended to remove the polyp. As an invasive procedure, colonoscopies do have risks, but complications are very rare.

In brief, while there are advantages and disadvantages to each approach, the most important thing is that you get screened.

Are certain tests more reliable than others?

All of the recommended tests are reliable for detecting precancerous polyps or cancer. There have been studies on each of the screening approaches that suggest that they decrease the risk of colorectal cancer and even save lives. However, to achieve these results, the frequency of the tests varies. A colonoscopy may need to be performed only every 10 years; whereas stool-based testing is recommended every one to three years, depending on the type of test used; and a colonography is recommended every five years.

How can cancer/precancer be detected in stool?

Precancerous polyps and cancers grow on the lining of the large intestine. These growths can cause microscopic bleeding and also shed cells into the stool. Stool-based tests use special techniques to detect either blood or abnormal genetic material in the stool. If a test returns positive, the patient is then sent for a colonoscopy to look for any abnormalities.

Why do stool-based tests need to be done more often than colonoscopies/CT exams?

While stool-based tests have good sensitivity for detecting colorectal cancer, they are slightly less sensitive for detecting precancerous polyps. Conversely, a colonoscopy can identify precancerous polyps at their earliest stage. As a result, depending on the findings of a colonoscopy, the screening recommendation may be as infrequent as every 10 years for average-risk patients.

Due to the pandemic, are you currently recommending at-home screening tests for people at average risk of colorectal cancer?

No single screening approach has been advocated over others in the setting of the COVID-19 pandemic. The ACS has advocated to maintain regularly scheduled screenings even for average-risk patients. The Centers for Disease Control and Prevention have provided guidance for how to conduct colonoscopies safely, and MUSC has implemented each of these safety measures. The best way to identify the right screening approach during this time is to discuss the options with your primary care provider.

Why is it important to stay up to date on colorectal cancer screenings, even in a pandemic?

Screening tests exist because precancerous polyps and even early-stage cancers generally do not cause symptoms. It is possible for someone to have cancer and not even know it. Because successful cancer prevention and treatment depends on finding precancerous polyps before they progress to cancer or on finding cancers at an early stage, it is very important that screening is performed in a timely manner according to medical guidelines.