Colon cancer blood test raises eyebrows

In July, the FDA approved a new blood test for colorectal cancer screenings that was able to detect 83% of Stage 1, 2 or 3 colorectal cancers in studies. 

But as Amol Akhade, MD, and medical oncologist, argues in an Aug. 27 commentary in Oncology News Central, the test is not accurate enough to surpass colonoscopies, long considered the gold standard in diagnosis. 

"Finding a blood-based test to screen for cancer is a dream for every oncology researcher. Imagine a simple blood test that can detect precancerous lesions or Stage 1 cancer in asymptomatic individuals," Akhade writes. 

"This would greatly benefit both oncologists and patients, potentially reducing cancer-specific mortality in the long term. The catch is that the test needs to be highly sensitive and specific to be clinically useful. Unfortunately, the recent approval of a blood-based colorectal cancer screening test by the FDA sets the bar too low, opening a dangerous Pandora's box," he added. 

Akhade argues that the study used for FDA approval presents "a significant dilemma" for oncologists interpreting test results. The recently approved Shield test has a 65% sensitivity to Stage 1 cancer alone, with a 10.1% false positive rate. Other noninvasive screenings had an 88% sensitivity for Stage 1 when using DNA for testing and 64% with fecal immunochemical testing. 

"Questions arise about the certainty of a negative test, the ability to reassure patients, legal and ethical responsibilities if a precancerous lesion or Stage 1 cancer is missed by this test, counseling for false-positive results, and the frequency of test repetition," he writes. 

While the non-invasive nature of these tests might mean that more people receive CRC screenings overall, Akhade maintains that questions about the tests' accuracy and ability to detect aggressive precancerous lesions sets the bar too low. 

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