Updated

Updated · Nebraska Medicine · Jul 16

FDA Approves Shield Blood Test for Colon Cancer Screening, but It Detects Only 13% of Precancerous Polyps

Updated

Updated · Nebraska Medicine · Jul 16

FDA Approves Shield Blood Test for Colon Cancer Screening, but It Detects Only 13% of Precancerous Polyps

Q: If the Shield test can't detect precancerous polyps, might its widespread use actually increase future cancer rates?

Yes—if Shield were widely used as a substitute for colonoscopy in people who would otherwise get colonoscopies, it could reduce cancer prevention and potentially allow more future cancers to develop. The reason is straightforward: colonoscopy does not just find cancer, it prevents it by detecting and removing precancerous polyps. Shield is designed mainly to detect cancers that already exist. The American Cancer Society says blood-based tests are not preferred because they are poor at finding precancerous growths. In the data cited in the news report, Shield detected only about 13% of precancerous polyps, compared with roughly 93% to 95% for colonoscopy, and it misses about 40% of stage 1 cancers. That does not mean Shield will automatically increase cancer rates overall. Its effect depends on who uses it. If Shield reaches people who refuse or cannot complete colonoscopy or stool-based testing, it could improve screening uptake and catch some cancers that otherwise would go undetected. In that group, it may lower harm compared with no screening at all. The risk comes if patients or health systems treat Shield as equivalent to colonoscopy. That could create false reassurance, leaving polyps in place to progress over time. Physicians and the ACS have been explicit that Shield is an alternative only for average-risk adults who decline other recommended options, not a replacement for colonoscopy. For prevention, colonoscopy remains the strongest tool.

2 articles · Updated · Nebraska Medicine · Jul 16

Shield became the first FDA-approved blood test for colorectal cancer screening, with the American Cancer Society recommending it only for average-risk adults who cannot or will not use colonoscopy or stool tests.
The guidance keeps colonoscopy as the preferred standard because Shield misses about 40% of stage 1 cancers and detects just 13% of precancerous polyps, versus 93% to 95% for colonoscopy.
Average-risk screening still starts at age 45, while people with family history, prior polyps or cancer, hereditary syndromes, inflammatory bowel disease, symptoms, or prior abdominal radiation are not candidates for Shield.
The blood draw requires no bowel prep or sedation and returns results in one to two weeks, but a positive result still requires colonoscopy and repeat testing is needed every three years.
The new option arrives as colorectal cancer remains the second-leading cause of U.S. cancer deaths, with ACS reporting rates falling in people over 65 but rising in younger adults.