New blood test for colon cancer is a mixed blessing
August 19, 2024
A blood test approved in August 2024 by the U.S. Food and Drug Administration (FDA) to screen for colorectal cancer may sound like a more convenient and preferable option to a more invasive and time-consuming colonoscopy or even an at-home stool test. But before you rush to judgment – or to your physician’s office to request this test – you need to know what it can and cannot do, particularly when it’s compared to screening tools already available.
The Shield blood test, which was recently approved by the FDA, detected 83% of colorectal cancers but only 13% of precancerous lesions, or polyps, in a clinical trial. The test correctly found all the later-stage cancers but only 65% of the earlier Stage 1 cases, research showed.
A major goal of the UT Southwestern Harold C. Simmons Comprehensive Cancer Center in Fort Worth at the Moncrief Cancer Institute is to detect cancer at the earliest stage to provide patients with the best chance for treatment and survival. As part of these efforts, the Moncrief Cancer Institute offers free cancer screenings to uninsured and underinsured individuals in 67 counties across Texas.
When it comes to colorectal cancer, several screenings that are much more effective than blood tests already exist, namely colonoscopies and stool-based tests.
The problem today is not a lack of screening methods. What’s more concerning is that as many as 40% of people between 45 and 75 years old are not up to date on their recommended screenings. And without screenings, colorectal cancer can grow undetected and become more difficult to detect at an early stage and to effectively treat.
That is where a blood test could provide some value because there are quite a few people who simply won’t consider getting a colonoscopy or taking a stool test. The American Cancer Society points out that getting screened, regardless of which screening tool you use, is the most important step you can take for your health.
I expect the blood-test cancer screening technology will improve over the next 10 to 15 years to provide an acceptable degree of accuracy. But right now, it should take a back seat to colonoscopy and fecal immunochemical testing.
Why should I care about colorectal cancer screenings?
Colorectal cancer is the third most common cancer in the United States and the second leading cause of cancer-related deaths among men and women combined.
Nationwide, more than 150,000 people are expected to be diagnosed with colorectal cancer this year. And while the overall rate of new cases has been dropping for decades, the risks to younger generations have been increasing about 1% to 2% every year since the 1990s. The death in 2020 of “Black Panther” star Chadwick Boseman at age 43 was a wake-up call to a lot of Americans about the rising number of young adults being diagnosed with colon cancer.
Related reading: 6 ways millennials and Gen Xers can reduce their colorectal cancer risk
Who is at risk for colorectal cancer?
Colorectal cancer is most often found in people over age 50 with the risk increasing as we age. But in May 2021, the U.S. Preventive Services Task Force (USPSTF) lowered the recommended age to start colorectal cancer screening from 50 to 45 because of the increase in younger people being diagnosed with the disease.
Family history, the type of screening, and previous screening results will all help determine how frequently you need to be tested. Check with your doctor about specific risks and what’s recommended for you. Factors that could increase your risk of colorectal cancer include:
- Obesity or overweight
- Type 2 diabetes
- A diet high in red meat, processed meats, or meats fried or grilled at high temperatures
- Tobacco use
- Alcohol use
- Inflammatory bowel disease
- Certain genetic mutations such as Lynch syndrome or familial adenomatous polyposis
What are my options for colorectal cancer screening?
Regular screenings are recommended for adults between 45 and 75 years old and selective screening for those older than 75 using one of the following methods:
- Colonoscopy
- Traditional colonoscopy
- Computed tomography colonography
- Flexible sigmoidoscopy
- Stool tests
- Fecal occult blood test
- Fecal immunochemical tests
- Cologuard (stool DNA test)
Traditional colonoscopy
Colonoscopy remains the most frequent option. It’s done on an outpatient basis under sedation to allow providers to inspect the entire colon and rectum using a tiny camera attached to a flexible tube, or endoscope. The test identifies any swelling, irritated tissues, polyps, or other signs of cancer. Colonoscopy is also a preventive measure because any suspicious masses or polyps will be removed during the procedure and biopsied.
Before a colonoscopy, you may be asked to refrain from eating certain foods for a couple of days. The night before, you’ll cleanse your colon by drinking a prescribed liquid that works like a laxative. This "prep" is probably the most dreaded and exaggerated aspect of colonoscopy, but it has come a long way in the last few years. The prep drink is gentler and tastes better, too.
The procedure itself is painless, quick, and very effective. Screenings are recommended every 10 years. Those at higher risk, including people with a family history of colorectal cancer and those who have had polyps detected in previous screenings, will need testing every five years.
Computed tomography (CT) colonography
This non-invasive procedure involves inflating the colon with air or gas and then using a CT scanner to capture images of the colon and rectum to look for suspicious polyps. A colonoscopy would be required to remove the polyps.
Flexible sigmoidoscopy
Considered a partial colonoscopy, a flexible sigmoidoscopy also uses a camera attached to an endoscopy. This exam inspects only the lower section of the large intestine. The procedure typically does not require sedation. Patients will likely need to restrict their diet a day before the procedure. Providers sometimes recommend a laxative, enema, or suppository before the procedure.
Stool tests
First approved by the FDA in 2014, DIY stool tests involve people collecting a sample of their stool at home or at their doctor’s office to be sent to a lab for analysis. Three different types of tests are available.
- Fecal occult blood test (FOBT), which looks for hidden blood in the stool. Certain foods will have to be avoided a few days before the sample is collected, and you may also need to stop taking certain medications, per doctor’s instructions. Tests are recommended annually.
- Fecal immunochemical tests (FIT) are similar to FOBTs, but they don’t require a change in diet. Tests are recommended annually.
- Cologuard (stool DNA test) looks for cancer-related DNA markers and hidden blood in stool. Tests are recommended every one to three years.
Some people may be turned off by the ick factor, but stool-based tests are a good option for people at average risk for colon cancer. The key is to follow the instructions when collecting and submitting the sample. A study published by UT Southwestern earlier this year found that 1 in 10 at-home tests could not be processed by a lab, mostly due to patient error.
A positive result from a stool test does not necessarily mean you have colorectal cancer. A colonoscopy can provide a definitive diagnosis.
What about doing a blood test?
Several blood tests that screen for certain cancer biomarkers are now available, and they require no advanced preparation. As mentioned earlier, however, the blood tests have a lower sensitivity, they are not included in the recommended screening methods, and any positive result would need to be confirmed by a colonoscopy.
- Shield blood test: Approved by the FDA in 2024, this test detects 65% of Stage I colorectal cancers, 100% of later-stage cancers, and about 13% of precancerous lesions, according to the manufacturer. The test is covered by Medicare but may not be covered by your health insurance. Out-of-pocket cost is $895.
- Epi proColon blood test: The first blood test approved for colorectal cancer screening in 2016, it looks for a specific type of DNA that is shed by colorectal cancer cells. It detects cancer about 70% of the time and costs $192 out of pocket.
- Galleri blood test: Not yet approved by the FDA, this test is available by prescription, and it can detect a molecular signal associated with more than 50 different types of cancer, including colorectal cancer. While it checks for many types of cancer, a positive signal requires further testing to confirm a diagnosis. It costs $949 and is unlikely to be covered by insurance.
Blood tests are probably best suited for patients who will not or cannot get one of the recommended and more effective colorectal cancer screenings.
What’s the bottom line?
The blood test recently approved by the FDA attracted a lot of attention, and it certainly won’t hurt to get one. But it’s important to understand that as a screening tool it is limited. And if you get a positive result, a colonoscopy will be required to confirm or rule out a cancer diagnosis.
If results from a blood test are negative, that doesn’t necessarily mean you are in the clear. It just means the test didn’t pick up any of the early signs of colorectal cancer.
Will there be a day in the not-so-distant future when a quick and reliable blood test will be able to screen patients for any number of cancers? Most likely, but we’re just not there yet.
To visit with a doctor or schedule a colorectal cancer screening, call 214-645-8300 or request an appointment online.
