Grail blood test detects multiple types of cancer

In 2021, Grail launched the first multi-cancer early detection test called Galleri. The test analyzes fragments of cell-free DNA shed by tumors in the bloodstream to identify any chemical methylation patterns that could indicate the presence of cancer.

In 2022, Grail released the findings of a trial involving 6,629 patients. At the time, interim data showed that the Galleri test was able to detect cancer signals in 92 participants, with 29 having cancers that were detected by additional tests, such as CT/PET scans and biopsies. Of these participants, 23 had new cancers, with nine being in the early stages, and six had previously had cancer and were experiencing a recurrence.

Since then, Grail has conducted a larger clinical trial of its test called Pathfinder 2. The trial included almost 36,000 participants ages 50 and older with no clinical suspicion of cancer from the United States and Canada.

Overall, the test was able to detect a cancer signal in 216 participants, and of these participants, 133 were diagnosed with cancer. The positive predictive value, or the likelihood of receiving a cancer diagnosis following a positive test result, was 61.6% — much higher than what was found in previous trials (43% to 50%). Of the new cancers detected by Galleri, over half were in stage I or II, and over two-thirds were in stages I to III.

For all cancers, the test had an episode sensitivity of 40.4% while its specificity was 99.6%, meaning that its false positive rate was just 0.4%.

When the test was combined with recommended screenings for breast, cervical, colorectal, and lung cancers, researchers found that there was a seven-fold increase in the number of cancers detected. According to Grail, Galleri was able to detect three times as many cancers when combined with standard screenings for different types of cancer. The company also noted that around 75% of the cancers detected by Galleri don't have standard screening options.

Commentary

Luis Diaz, head of solid tumor oncology at Memorial Sloan Kettering Cancer Center, said the results from Grail's latest trial were an encouraging improvement from its earlier Pathfinder study. He also noted that it was helpful to see how the test performed in a more diverse population.

"To me, it's meaningful," Diaz said. "It shows that the [technology] is moving in the right direction, and I think it's good for the space. It increases the bar."

However, Ruth Etzioni, a biostatistician who studies cancer screening, said it was unclear whether the cancer cases Galleri detected were actually caught earlier than they would have been otherwise with more traditional screening methods.

"It's very difficult to judge the clinical importance of these results," Etzioni said. "The extent to which the fate of these cancers is being changed by being diagnosed by the test is unclear."

Some researchers also warned that early detection of cancer may not necessarily lead to better survival outcomes for patients. Blood tests for cancer may also lead to overdiagnosis, which can lead to unnecessary treatment for tumors that ultimately end up being harmless.

"We will dip more and more deeply into the iceberg of disease" and find "lesions that look like a cancer to the pathologist but may not have the same natural history at all," said Barnett Kramer, a member of Lisa Schwartz Foundation for Truth in Medicine and a former director of the National Cancer Institute's division of cancer prevention.

"Everybody loves early detection, but it comes with harms," said Donald Berry, a statistician at MD Anderson Cancer Center. "The harms, we know. The benefits are very uncertain."