The positive predictive value, however, was less straightforward. In first responders, Dr. Shukla found that only half of positive Galleri tests were confirmed cases of cancer. And an analysis of Grail’s data found that only 38% of positive Galleri tests – 35 of 92 tests – represented a validated cancer diagnosis.
“In a clinical setting, positive predictive value is more usable for decision-making for the patient,” said Dr. Lee. “Positive predictive value isn’t always high, because everything doesn’t always transfer perfectly to the clinic.” But in the general population, if only 38% of patients with positive Galleri results truly have cancer, the test is “not quite useful to make a decision for the patient or the providers.”
Galleri may also be a costly prospect for patients, no matter the result, cautioned Electra Paskett, PhD, an epidemiologist and cancer screening expert at Ohio State University, Columbus. A positive Galleri test leads to a cascade of follow-up diagnostic tests, which payers may not cover. For a negative result, Galleri recommends that the patient undergo screening again in a year, at an annual cost of $950 plus the cost of any follow-up testing when Galleri does pick something up.
“If a provider wants to offer the Galleri test, all those things need to be made abundantly clear, in my opinion,” Dr. Paskett said.
Following the negative Galleri test, Mr. Arenz’s cancer didn’t slip through the cracks because he received other advanced imaging free of charge. But whether all doctors will go to such lengths to back up Galleri results, even for patients with negative results, is unknown.
A negative result can give patients “a huge false sense of security,” said Dr. Shukla. And if a test is positive, the workup isn’t simple. Chasing cancer, especially one that’s not really there, can be nerve-wracking and expensive.
The question, then, is why perform the Galleri test at all if results require so much validation?
Dr. Parikh explained that a high-risk group such as firefighters represents an ideal-use case for Galleri and other liquid biopsy tests. But she noted that she would be “wary of the ability of the system to manage this test en masse” were the test to be used more widely in the general population.
Dr. Shukla said it’s less about the results she’s getting today and more about making the test more effective for her patients in the future. First responders need a test such as this that can quickly identify multiple cancers. However, to improve the test, Grail needs more data from this high-risk population. That’s what she’s after.
Mr. Curtis doesn’t regret taking the Galleri test. The emotional toll of thinking he had cancer for a few days wasn’t too high a price, in his opinion. It’s part of cancer screening. But he acknowledged that it would have been a much more burdensome experience had he’d been financially responsible for the workup or if he hadn’t had Dr. Shukla to manage his case from start to finish.
Because it was free, Mr. Arenz doesn’t regret undergoing the Galleri test either. But he tells his coworkers to check the site, do their research, and get more screening.
“Any medical center that’s just doing this one test, you just have to be careful,” Dr. Shukla said. “It’s not that easy.”
A version of this article first appeared on Medscape.com.