A blood test to detect multiple forms of cancer received support Wednesday from a federal health panel, one day after a Mayo Clinic-led study showed it discovered undiagnosed cases of lung, breast, colon and other cancers.

The results raise hopes that a single test could one day replace multiple tests, such as mammograms for breast cancer and colonoscopies for colon cancer. For now though it augments existing tests and can find evidence of cancers for which routine screening isn’t recommended.

What happened

Research led by Mayo’s Dr. Karthik Giridhar found 173 cases of cancer by giving 32,007 clinical trial participants the blood test, known as Galleri and made by California-based Grail, Inc.

Results of the PATHFINDER 2 trial were published Tuesday in Nature Medicine, a scientific journal, and presented Wednesday to an advisory panel of the Food and Drug Administration.

Giridhar told the FDA panel that the results validated the test and its ability to identify cancers that otherwise wouldn’t have been found until deadlier stages.

“This test is preferentially finding the higher-risk cancers we otherwise miss until symptoms emerge,” he said.

The advisory panel voted 7-2 that the benefits of Galleri outweigh its risks, but stressed it should not substitute for other recommended screenings, and that a negative result doesn’t mean someone is free of cancer risks.

Some voted no because of the lack of evidence so far that the test can help save lives, not just find cancer. FDA officials will weigh the evidence, including the advisory panel’s recommendation, and decide whether to grant Grail’s request to approve the test for wide distribution.

By the numbers

The test identified a risk in 287 trial participants, all 50 and older, but only 173 had cancer, according to the Mayo-led study. That meant the test’s positive predictive value was 60%.

Researchers weighed how often the test missed cancers by waiting 12 months to see if malignancies emerged. The 267 cancers that emerged in participants with negative results meant that it was 99% effective at ruling out cancer risks for one year.

Galleri appeared more effective at picking up cancers of the lung, liver and ovaries and less effective at detecting them in the skin, bones and blood, results showed.

The test also was unsurprisingly better at finding cancers that had progressed to more severe stages. But Giridhar said it also didn’t pick up minor malignancies.

“We’re not picking up ... the type of cancer (that) patients might die with rather than from,” he said. “This mitigates the risk of overdiagnoses.”

Three-fourths of the cancers identified were those for which other screening tests are not recommended. However, the test also found breast and colon cancers in patients between scheduled screenings. A colonoscopy is recommended once every 10 years, for example, for people 45 to 75 at average risk for colon cancer.

What this means

Galleri is available out-of-pocket for around $900 under special federal regulations for certain tests, but FDA approval would pave the way for coverage by Medicare and perhaps private insurance.

President Donald Trump earlier this year signed legislation that would hasten Medicare coverage once the FDA approves any multicancer early detection (MCED) test, such as Galleri.

Approval of Galleri would likely result in a rush of more MCED tests to market.

FDA panelists were sensitive to the precedent set by their vote, debating whether they should set an upper age limit for testing in addition to the lower age limit of 50. They also weighed patient anxiety from false positives, when the test indicates cancer may be present when it’s not.

“It’s really important that it is appropriately rolled out and everybody is aware of its intended use,” said Dr. Aditya Ghosh, a Mayo internist and the lone Minnesotan on the FDA advisory panel. He voted in support of Galleri.

The conversation

Two critics told the FDA panel to discourage the description of Galleri as a test for “early cancer” because it was most effective at finding later-stage diseases.

Test results will produce overreactions — from patients who “freak out” over false positives to those who use all-clear results to skip recommended screenings, said Diana Zuckerman of the National Center for Health Research, a health policy think tank.

“They will be told to continue with other screening. Will they?” she said.

Cancer survivors told the FDA panel that the test probably saved their lives. Dr. William Dahut of the American Cancer Society said “no screening test is perfect” but Galleri is worth advancing.

“They all have false positives. They all miss cancers,” he said, “and they’re all going to improve over time.”

Our reporting says

Existing screenings received praise this week when federal data showed U.S. cancer deaths continued to decline.

Minnesota has above-average rates of colon and breast cancer screenings, which partly explains why the state has a higher incidence of cancer but a lower death rate.

The question is: Will more cancer screening options produce better results or more confusion? (Similar concerns emerged when Mayo research produced the Cologuard stool sample test as a way to screen for colon cancer besides colonoscopies.)

FDA panelists voiced fears that the test is ripe for overselling and overuse. Giridhar countered that the test is already available to people who can afford it, but FDA approval would improve access for those who need it.

“A two-tier system, where early detection is a function of income rather than clinical need, is already forming,” he said.

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