FDA Approves First Blood Test for Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer and the second leading cause of cancer-related deaths worldwide, making early detection critical for improving outcomes1 2. In July 2024, the U.S. Food and Drug Administration (FDA) approved the first blood-based test, called Shield, for colorectal cancer screening in average-risk adults aged 45 and older3 4. This approval marks a significant advancement in CRC screening, offering a noninvasive alternative that may increase screening adherence among those reluctant to undergo colonoscopy or stool-based tests5 .

Blood Test for Colorectal Cancer Detection

The newly FDA-approved Shield test is a blood-based screening tool designed to detect colorectal cancer by identifying tumor-specific DNA mutations circulating freely in the bloodstream, known as circulating tumor DNA (ctDNA) 16. ctDNA contains cancer-specific genetic alterations that distinguish it from DNA derived from normal cells, enabling the test to specifically detect colorectal tumors7 . Shield is currently the only FDA-approved blood test for CRC screening in average-risk individuals and is recommended to be performed every three years starting at age 458 .

“Having a simple blood test for colorectal cancer that could be added to a routine medical visit is a major step toward closing the screening gap.”

— Asad Umar, D.V.M., Ph.D., National Cancer Institute3

• Shield analyzes cell-free DNA (cfDNA) in the blood, focusing on mutations and alterations associated with colorectal cancer3 1.
• The test is tumor-specific, minimizing false positives from non-colorectal cancers6 .
• It detects DNA fragments shed by cancer cells or large precancerous polyps into the bloodstream9 .
• A positive Shield result indicates a high likelihood of colorectal cancer or advanced adenomas, requiring follow-up colonoscopy for confirmation and polyp removal10 6.

Clinical trials involving nearly 8,000 participants demonstrated that Shield detects colorectal cancers with 83% sensitivity and 90% specificity in average-risk adults11 3. Sensitivity refers to the test’s ability to correctly identify those with cancer, while specificity measures how well it excludes those without the disease4 . Shield’s performance approximates that of established stool-based tests such as the fecal immunochemical test (FIT) and multitarget stool DNA tests like Cologuard12 11.

Despite its promise, Shield has notable limitations. It is less sensitive for early-stage colorectal cancers, detecting about 65% of Stage I cancers, and has poor sensitivity (approximately 13%) for precancerous polyps, which are important targets for cancer prevention15 34. Colonoscopy remains the gold standard because it allows direct visualization and removal of these precancerous lesions, thereby preventing cancer development13 3.

• Shield is intended as a primary screening option for average-risk adults aged 45 and older10 1.
• Positive Shield results must be followed by colonoscopy to confirm diagnosis and remove polyps, as the blood test cannot detect or remove precancerous growths6 3.
• The test offers a less invasive alternative that may improve screening uptake among individuals who avoid colonoscopy or stool tests due to discomfort or inconvenience5 10.
• Shield is covered by Medicare, making it accessible to a broad population16 10.

• It is recommended to be repeated every three years, aligning with current colorectal cancer screening guidelines17 8.

• Less than half of individuals with positive Shield results currently undergo timely follow-up colonoscopy, limiting the test’s overall effectiveness4 .

• Research is ongoing to develop multi-analyte blood panels and novel biomarkers to improve early detection of both cancer and precancerous lesions18 1920.
• Experts emphasize that while Shield does not replace colonoscopy, it represents a major step toward closing the colorectal cancer screening gap by offering a convenient option during routine medical visits3 10.