There’s nothing ‘simple’ about a blood test for cancer

“If you ever hear about a simple blood test run for the hills because there is no such thing.”

That’s the advice from health journalism watchdog Gary Schwitzer, publisher of  a website aimed at helping the public assess health claims reported in the media.

Yet the promise of a simple blood test seems irresistible.

A quick Google search reveals a series of headlines over the last few months heralding the development of simple blood tests to find ovarian cancerskin cancerinflammatory bowel diseaseconcussions,PTSDdepression and Alzheimer’s — even though none of those tests is on the market yet.

And last week there was a new flurry of news stories announcing another simple blood test — this one reporting the ability to detect eight different types of cancer.

“The test isn’t as good as the news reports would have you believe,” said Dartmouth professor Dr. Gilbert Welch, who has written about the limitations of any blood test that claims to detect cancer.

“This is fundamentally a really hard problem to detect the right mix of biomarkers and cell free DNA that’s predictive of an important cancer.”

The blood test, called CancerSEEK, is still in the early research stages of what will be a long and challenging development process. Yet those nuances were overshadowed by the excited headlines about a “breakthrough” blood test.

“I don’t think there’s any question that the miscommunication of screening tests has been the most prevalent and troubling trend that I’ve seen by leading news organizations,” said Schwitzer.

‘Messy area’

Even if that test was on the market, there would be nothing simple about it.

“As a population-based screening tool I think it’s a total Pandora’s box,” said Welch.

It would raise a series of ethical and clinical quandaries. How many actual cancers does it miss? How many false cancers does it detect?  And what does a positive result mean if there are no detectable tumours or other anatomical abnormalities?

“I fear that the minute people hear that they have a blood test compatible with cancer and the doctors in the front line can’t find it that’s going to be a terrible thing. I fear it will be very hard to put this to rest,” said Welch.

One risk is that widespread screening for cancer will turn healthy people into cancer patients.

Welch points to the controversies over the PSA test for prostate cancer, which discovers cancers which might never be dangerous yet could lead to patients being exposed to harmful side effects from treatment, including impotence and incontinence.

“The simple blood test to detect prostate cancer raised some of the most complex issues in medicine,” Welch said, adding that some of the early enthusiasm for widespread cancer screening is starting to wane.

“I think more and more of the medical community realize it’s a much more messy area than we originally imagined,” he said. “I think we originally imagined that any effort to diagnose a disease early would only help people, it wouldn’t hurt them.”

Still, Welch said the overall research into looking for cancer markers in blood is a valid area of study.

“I think there’s some settings where this makes a great deal of sense. I think it’s one thing in people with established cancers to use this kind of test and monitor their response to treatment or see whether their cancer is coming back. In that kind of surveillance or tailoring of therapy it may be very useful to be able to do that with a blood test.”

But rather than hyping the promise of a test that is not ready for prime time, the media should emphasize all the caveats and limitations.

“How many medical centres globally are getting phone calls or having patients asking for visits right now in response to stories like this?” said Schwitzer.
By Kelly Crowe
Photo credit: BENCHAMAT/Shutterstock.
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