ROCHESTER, MINNESOTA — Biotechnology company Grail reported in February that the largest trial to date of a multi-cancer blood test failed to achieve its primary objective, showing no measurable reduction in advanced cancer diagnoses among people who received its Galleri test compared with those who did not. Grail says the Galleri test can detect more than 50 types of cancer by measuring DNA fragments in the blood.

In some cancer types, the Galleri test appeared to detect more cancers at the earliest stages and saw a decrease in the number of stage 4 diagnoses. The full results of the trial have not yet been published. Grail will continue to follow patients from its trial for up to eight years after their first test to monitor any reduction in deaths.

Cancer blood tests pick up tiny amounts of DNA circulating in the blood. Research on multi-cancer blood tests has progressed to scrutinizing those DNA amounts and feeding the data into algorithms that can highlight changes suggestive of cancer. Researchers hope such a test could accurately detect a range of cancers at early, still-curable stages, translating into lives saved.

Dr. Aadel Chaudhuri, a radiation oncologist at the Mayo Clinic in Rochester, Minnesota, who is researching multi-cancer blood tests, said: "It's amazing we can even do this. If you had asked me 10 years ago, my answer would have been 'It's not feasible.' If we're thinking of DNA shed from a small tumor, it's like being on the beltway in D.C. and you're looking for one Volkswagen."

Chaudhuri also addressed the trial outcome. "It's hard to argue that it wasn't a setback," he said. "Clinically, what I truly care about is a decrease in stage 4 cancers."

Dr. Deb Schrag, a medical oncologist, said that for multi-cancer blood tests like Galleri to be seen as a paradigm shift by the medical profession, they will need to demonstrate that they can help save lives. Schrag said that some cancers might release detectable amounts of DNA into the bloodstream because they are highly aggressive, and that even if a test detects such tumors sooner, early detection may not guarantee they will be more treatable.