Questions remain about how to interpret MCED test results. Only some blood tests can pinpoint which organ the cancer is actually in. Lab tests must be run on potentially cancerous tissue to confirm a diagnosis, but you can’t biopsy someone’s entire body. False positives remain an issue for the entire field of cancer screening, which, by design, involves sifting through mounds of healthy tests to find cancer. Galleri—the MCED furthest along the path to widespread use—incorrectly flagged 57 healthy blood samples as cancerous in the aforementioned study.
There’s also a risk of jumping the gun—some cancers never become invasive or life-threatening, but early detection could prompt harsh treatment like chemotherapy. Some data suggests that less worrisome cancers actually show up in the bloodstream less, which could minimize that problem.
The NIC trial will help determine how blood test results for cancer should be interpreted, and it should provide a standard approach to launching cancer screening studies as companies flood the field with new tests.
“I don’t think most companies tend to want to compare their tests head to head,” says Timothy Rebbeck, a professor of cancer prevention at Harvard. “It’s expensive and difficult. So somebody else, a neutral party like the NCI, needs to.”
Rebbeck thinks the blood tests the new trial will vet will prove most helpful in the cases of pancreatic, liver, and ovarian cancer, which kill often and have no other form of screening. Still, longer trials are needed to confirm whether the time bought by these blood tests saves lives.
But Rebbeck is optimistic about the Cancer Moonshot’s ultimate goal: “It seems very realistic to me to think that we could reduce death by half,” he says.