Can we use a blood test to screen for colorectal cancer?
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A new blood-based screening option for colon cancer was just approved by the FDA, so in this episode, the 2 minute update looks at the study evaluating the effectiveness of that test.
This study included 7861 patients at average risk for colorectal cancer. Everyone was at least 45 years old, and everyone had a colonoscopy and a blood test that looks for cell-free DNA consistent with colon cancer.
The study excluded anyone with a history of colon cancer or at high risk for colon cancer, and they also excluded anyone who was not yet due for colon cancer screening. The results of the blood test were compared to the findings from the colonoscopy, which was considered the gold standard to detect colorectal cancer.
The blood test showed a sensitivity of 83.1% compared to colonoscopy, with a specificity of 89.6%. To put that in perspective, the blood test appears to be more sensitive but less specific than fecal immunochemical testing. Compared to stool DNA and RNA tests, the blood test is a bit less sensitive, and the specificity is pretty similar. The stool RNA test was approved by the FDA in March, 2024. Comparisons should be interpreted considering that some of the analyses looked as slightly different outcomes, such as advanced precancerous lesions or staging for cancer.
Unfortunately, over 50,000 Americans die each year from colon cancer. If colon cancer is found while it is localized, 5 year survival is 91%. That plummets to 14% with metastatic disease. But only about 60% of eligible people are screened. There are lots of barriers to screening, but patients seem to have no problem with simple blood draws.
This test is called Shield, and is FDA approved. It’s covered by Medicare at a 3 year interval. It’s currently pretty expensive – the cash pay price is $895. But if the price comes down, and if the USPSTF recommends it, it might be the option that patients will readily accept.
References: Chung et al. A Cell-free DNA Blood-Based Test for Colorectal Cancer Screening. NEJM 2024:973; Imperiale et al. NEJM 2024;390:984; Barnell et al. JAMA 2023;330:1760