The idea of taking one blood test that tests for multiple cancers, a called a “liquid biopsy” in the medical-testing business, is a tempting one. If they work as promised, the tests check your blood for traces of various types of cancer before you even show any symptoms. The problem with these tests, meant as an option for very early cancer screening, is that they’re available, and even marketed directly to consumers, even though they haven’t been shown to actually be effective.

There are tumor-screening blood tests in wide use, the best-known of which is the PSA (prostate-specific antigen) test given to men starting around age 50, or younger if they’re at higher-than-average risk for prostate cancer. That’s a routine screening test, making the idea of blood tests that screen for signs of multiple cancers at once seem plausible. While it might be someday, the problem is that we don’t yet have proof that such tests work.

Direct-to-consumer lab testing has been in the news recently because of the problems at Theranos, a company that aimed to make blood testing easier, cheaper, and available at the corner drugstore.

After problems with the accuracy of Theranos’ tests led to regulatory problems and sending out thousands of revised test results, Walgreens severed its relationship, ending what both companies hoped might be a nationwide partnership. The problem is that tests that are designed and performed in a single lab have been regulated very loosely by the Food and Drug Administration, which developed the regulations with hospital tests in mind. They probably didn’t picture tumor tests marketed to the public 40 years ago.

That’s what the company Pathway Genomics used to sell, and the sales pitch speaks to you on a deep level if cancer runs in your family. The FDA took issue with the company’s marketing, which used the prevalence of cancer to sell test kits. The problem, the agency noted, was that the science the company cited to sell its tests didn’t really prove what they claimed: that the tests would catch early cancerls in people with no other symptoms.

“It is unclear how the literature that you cited, addressing the presence of circulating tumor DNA (ctDNA) in already-diagnosed patients, is adequate to support the expansive claims of screening for early cancer detection using ctDNA in undiagnosed patients for up to 10 different cancers with the CancerIntercept(TM) Detect,” the FDA said in a letter to the company last fall. Since then, Pathway Genomics has toned down its marketing language, and is now publicly recruiting test subjects for a clinical trial of their blood test.

Startups selling new blood tests directly to consumers raise safety and accuracy concerns [Chicago Tribune]

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