New Grail cancer test data shows progress but raises questions

As part of its bid to transform the future of cancer screening and take control of a potentially large and increasingly competitive market, Grail on Friday announced new data from a large U.S. study of its flagship blood test for detecting dozens of tumor types. The results reinforce some of the company’s arguments for a new approach to screening; Experts said the company appears to have improved the test’s accuracy, but noted that major questions about the real-world impacts of such tests remain.

The Pathfinder 2 study recruited nearly 36,000 adults over the age of 50 to evaluate the biotech’s screening test, Galleri. When researchers measured the test’s performance in participants followed for more than a year, they found that it detected 40.4 percent of cancer cases, a characteristic of the test known as sensitivity. Just over half of these cancers were detected early, at stage 1 or 2, and about three-quarters of them are not part of current screening programs, such as pancreatic, liver, and head and neck cancers.

Of the patients who tested positive, nearly 62% actually had cancer, while 38% of the positive results were false alarms. In previous studies, Galleri’s positive predictive value was somewhat lower, ranging from 43% to 50%.