Detect cancer with simple blood test?

Detecting cancer with simple blood test has been a dream for doctors. Because of the validity of tests (false positive and false negative issue) and lead time bias (detection cancer early does not always get the cancer cured) however, it has not been effective to use a blood test to detect cancer for the general population. Doctors attempted various tumor markers. These are examples of tumor markers:

  • Alpha-fetoprotein (AFP, α-fetoprotein) for liver cancer
  • Carcinoembryonic antigen (CEA) for colorectal cancer.
  • Prostate-specific antigen (PSA) for prostate cancer.
  • CA19-9 (carbohydrate antigen) for pancreatic cancer.
  • Cancer antigen 125 (CA 125) for ovarian cancer.

In turned out, however, tumor marker are mostly not useful in detecting cancer for an average, otherwise healthy person. Tumor markers are effective only to follow up known cancer patients.

The advent of gene medicine or precision medicine allows doctors to use more tumor markers. Because some cancers are closely related to mutation of certain genes, effort to detect cancers by detecting those genes make sense. Startups like Pathway Genomic claims that cancer mutation blood test can be used “in early screening tool for the potential early detection of specific cancer types in patients who have not been diagnosed but are at an increased risk.”

I think, however, there is a long way to go before cancer mutation blood tests  can be used more widely. Same issues that made the traditional tumor markers useless can be even more rampant in cancer mutation blood test. The Food and Drug Administration also concerned about the premature use of cancer mutation blood test. In its letter to Pathway Genomics, the maker of CancerIntercept, an FDA official wrote, “It has come to our attention that you are currently marketing CancerIntercept Detect, which is a non-invasive blood test intended for use as a screening tool for the early detection of up to 10 different cancer types in high-risk populations. … We have conducted a review of our files and have been unable to identify any Food and Drug Administration (FDA) records reflecting the approval, clearance, or listing of these devices. … Based on our review of your promotional materials and the research publication cited above, we believe you are offering a high-risk test that has not received adequate clinical validation and may harm the public health.”

 

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