How do colorectal cancer screenings measure up?
Colorectal cancer is the third most common cancer diagnosed in the United States, according to the American Cancer Society (ACS). Colorectal cancer includes both cancer of the colon and cancer of the rectum. But it doesn’t just appear overnight. It starts as a small growth called a colon polyp and develops into cancer. This process can take 5 to 10 years to happen.
We tend to start seeing colorectal cancer in people who are 60 and older, so we recommend people start getting screened for colon polyps at age 50. Your doctor may recommend starting earlier if you have certain risk factors, including a family history of colon cancer. Because of their increased risk, we also recommend African-Americans start getting regular colonoscopies at age 45. The idea is to find colon polyps early and remove them before they have a chance to develop into cancer.
The gold standard for colorectal cancer screening is the colonoscopy. It’s an accurate, effective test that lets us check patients for colon polyps and colorectal cancer. People who have regular colonoscopies may reduce their risk for getting colorectal cancer by 40 percent. But getting ready for a colonoscopy can be a hassle, and some patients would rather have an alternative to this test.
There are additional tests available for colorectal cancer. One that’s been getting some attention recently is Cologuard, which is a test people can take at home with a doctor’s prescription.
Though some say these alternative tests are just as effective as colonoscopies, I want to emphasize one important fact: These alternative tests look at different factors than what colonoscopies look at. That’s why it’s important to follow your doctor’s advice and get screened for colorectal cancer according to the current medical guidelines.
How a colonoscopy works
Before someone has a colonoscopy, we first have to prepare the colon for the procedure. This involves the person having the test limiting their diet to clear liquids the day before the test. The person also has to clear the bowels before the test by taking special laxatives.
The test itself is fairly simple. We pass a thin, flexible tube called a colonoscope through the rectum so we can see the inside of the colon on a monitor. The patient is usually asleep during the test. For some patients, we use conscious sedation, which relaxes the patient but allows us to give the patient instructions during the test.
The test itself usually takes about 20 minutes to complete, but preparing for it and recovering afterward could mean the patient has to take a day or two off work. Missing work is one of the complaints I hear about colonoscopies most frequently, along with the bowel preparation. Most people don’t mind the colonoscopy procedure itself. In fact, because of the sedation we use, most people don’t remember the test at all. Most people only need a colonoscopy every 10 years.
Other tests for colorectal cancer
Most other types of tests for colorectal cancer are what we call stool tests. Rather than looking directly at the colon for evidence of colorectal cancer, stool tests use a stool sample the patient provides. Stool tests have a higher sensitivity for finding colorectal cancer that has already developed. They aren’t as good as colonoscopy for finding colon polyps. There are several types of stool tests, including:
- Hemoccult test
- Fecal immunochemical test
In a hemoccult test, a doctor gives the patient six cards that the patient uses to collect three stool samples. The patient mails these cards to the doctor, who checks the samples for a molecule in blood called heme. Heme is a component of hemoglobin, which carries oxygen in the blood. Finding heme in a hemoccult test is a possible red flag for colon cancer.
Hemoccult tests have a few problems. They’re not very sensitive, so they can miss some conditions. And they can result in false positive results, or results that identify a condition that doesn’t actually exist, if there’s any bleeding in the digestive system.
Fecal immunochemical test
A fecal immunochemical test, or FIT, uses a chemical protein to detect hemoglobin in a stool sample. FIT is a much more sensitive test than the home hemoccult test. One reason for this is that hemoglobin molecules are broken down by the body during digestion. This means that if FIT detects hemoglobin in a stool sample, it’s easier for us to eliminate the stomach or other areas of the digestive system as sources for the blood.
FIT is typically done on an annual basis. Doctors in some areas without ready access to colonoscopy technology might use FIT as an alternative to patients getting regular colonoscopies.
Cologuard is one of the newest tests developed for colorectal cancer. It’s approved by the Food and Drug Administration (FDA) for people who don’t want other forms of colorectal cancer screening.
Cologuard combines FIT with a test for DNA markers. These markers can get mixed in with stool as it moves through the colon. When a patient sends a stool sample to a lab for a Cologuard test, the lab looks for mutations in the DNA that happen in cases of colorectal cancer. If the test is positive for these mutations, the lab recommends that the patient get further testing for colorectal cancer. Unlike the annual FIT, patients only need to retake the Cologuard test every three years.
The problem with alternatives to colonoscopy
Because of how these alternative tests work, they may find colon problems that are more advanced than we would find if we had done a colonoscopy earlier in the process. Early detection is key to surviving colorectal cancer.
As the ACS notes, about 92 percent of people with stage I colon cancer survive at least five years. For stage IV cancer, that rate drops to about 11 percent. And, of course, our ideal goal is to catch colon polyps before they ever turn into colorectal cancer in the first place.
Another issue with alternative tests is that they may not be effective in helping people avoid colonoscopies—which is a primary goal for many patients. If any of these tests yields a suspicious result, the next step is for the doctor to order a colonoscopy to see if the test’s result was accurate. So avoiding a colonoscopy with one of these tests could just lead to needing a colonoscopy anyway. If that’s the case, why not just have the colonoscopy to begin with?
Practical realities of colorectal cancer screening
I know not everyone who should have a colonoscopy is going to have one. The American Society for Gastrointestinal Endoscopy notes that more than 60 percent of Americans age 50 or older haven’t been screened at all for colorectal cancer. And that number is probably higher in some areas and parts of the population.
In D.C. for example, we discovered a high instance of late-stage colon cancer exists among African-Americans in Ward 5. To help combat this, we launched the “Colon Cancer Prevention in the Neighborhood” program. Part of the former Vice President Joe Biden’s Cancer Moonshot, we’re working to increase colon cancer education in Ward 5, perform risk assessments and distribute fecal immunochemical tests that residents can do at home.
Most people go with their doctors’ recommendations for screening. But some people, for various reasons, just refuse to have a colonoscopy. In that sense, the best screening available for colorectal cancer is one that a person will have. If one of the alternative tests finds something that motivates a patient to get a colonoscopy, and we’re able to detect and treat that person’s condition, then that’s what I care about.
Personally, I’m going to continue recommending that my patients get regular colonoscopies according to the standards of care. But if the alternative tests lead to more people getting screened and treated for colorectal cancer, that would be a great thing in my opinion.
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