Questions remain about how to interpret MCED test results. Only certain blood tests can identify in which organ the cancer is actually located. Laboratory tests must be done on potentially cancerous tissue to confirm a diagnosis, but a person’s entire body cannot be biopsied. False positives remain a problem for the entire field of cancer detection, which by design involves sifting through reams of healthy evidence to find cancer. Galleri, the MCED furthest down the road to widespread use, incorrectly flagged 57 healthy blood samples as cancerous in the aforementioned study.
There’s also the risk of jumping the gun: Some cancers never become invasive or life-threatening, but early detection could lead to harsh treatment like chemotherapy. Some data suggest that less worrisome cancers actually show up less often in the bloodstream, which could minimize this problem.
The NIC assay will help determine how blood test results for cancer should be interpreted and should provide a standard approach for 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 is expensive and difficult. So someone else, a neutral party like the NCI, needs it.”
Rebbeck believes that the blood tests that the new trial will verify will be most useful in cases of pancreatic, liver and ovarian cancers, which often kill 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 cut death in half,” she says.