Daijiworld Media Network - New Delhi

New Delhi, Oct 1: A blood test designed to detect signals from multiple types of cancer has shown promise in a large study involving nearly 36,000 adults, although researchers say further trials are needed to determine whether the technology can ultimately reduce cancer deaths.

Results from the PATHFINDER 2 study, published in Nature Medicine, involved 35,878 adults aged 50 and above in the United States and Canada who had no clinical suspicion of cancer and had not been diagnosed with or treated for cancer during the previous three years.

The study evaluated the Galleri multi-cancer early detection test, which analyses chemical patterns in fragments of DNA circulating in the blood. When a cancer signal was detected, the test also predicted the likely tissue or organ where the signal originated, helping doctors determine where to begin further diagnostic testing.

Among 32,007 participants with a full 12 months of follow-up, 287 received a positive test result. Of these, 173 were subsequently diagnosed with cancer. This resulted in a positive predictive value of 60.3%, meaning that about six in 10 positive results were associated with a cancer diagnosis during the study period.

The test had a specificity of 99.64%, while its negative predictive value was 99.2%. Overall, cancer was detected in 0.54% of participants, equivalent to about one cancer diagnosis for every 185 people screened.

However, the test did not detect every cancer. Its 12-month episode sensitivity was 39.3% across all cancers. The figure rose to 69.8% for a predefined group of 12 cancers responsible for a large proportion of cancer deaths, including cancers of the pancreas, liver, colorectal tract, stomach and other organs. Researchers noted that sensitivity varied considerably by cancer type.

The test's overall sensitivity was affected by cancers such as breast and prostate cancer, for which established screening methods already exist. The researchers therefore stressed that a multi-cancer blood test should not be considered a replacement for recommended screening procedures.

Among cancers detected through the test, 53% were diagnosed at stage I or II, while about 71% were diagnosed at stage I, II or III. The study also found that the test's prediction of the likely origin of the cancer signal was accurate in 91.3% of cases.

A major potential benefit of the technology is its ability to detect cancers for which there are currently no widely recommended screening tests. The study found that many of the cancers identified through the blood test belonged to types that are not routinely screened for in the general population.

The researchers also examined the safety of follow-up investigations. Among 35,335 participants included in the safety analysis, 213, or 0.6%, underwent an invasive procedure following a positive test result. About 90.5% of those procedures were nonsurgical, such as biopsies or endoscopic examinations.

For participants who were ultimately diagnosed with cancer, the median time between receiving the blood-test result and confirmation of the diagnosis was 37 days.

The findings come alongside results from the separate NHS-Galleri randomised controlled trial in England, which evaluated the same type of multi-cancer blood test among more than 142,000 people aged 50 to 77. Across three annual screening rounds, the test showed high specificity, but its sensitivity for detecting cancer remained limited.

Importantly, the NHS-Galleri trial did not meet its primary endpoint of reducing the incidence of stage III or IV cancers. Researchers have therefore cautioned that demonstrating the ability to detect cancer earlier is not enough by itself to establish that the tests improve survival.

The PATHFINDER 2 researchers said longer follow-up and further studies are required to determine the clinical benefits of multi-cancer early detection testing.

For now, the blood test is being studied as an additional screening tool rather than a replacement for established cancer screening. Mammograms, colonoscopies, cervical cancer screening and other recommended tests remain important because the multi-cancer test can miss cancers.

The findings nevertheless provide one of the largest prospective assessments so far of a blood-based test designed to detect multiple cancers in people without symptoms, offering further evidence about both its potential and its current limitations.