Detecting cancer years before symptoms appear is currently very difficult, but that may soon change after scientists developed a revolutionary new blood test. The blood test, which was created by researchers in China, is able to pick up cancers up to four years before symptoms appear, researchers say.

It is claimed that the test detects cancer in 95 percent of individuals who have no symptoms but later receive a diagnosis. They said the test was unlikely to be predicting cancer but rather picking up on cancerous growths that had not yet caused symptoms or been spotted by other methods. Such tests, known as liquid biopsies, have become the focus of much research as they offer a non-invasive way to screen patients.

The new test was based on screening particular regions of DNA found in blood plasma for telltale tags, called methyl groups, that often crop up in tumor DNA. They then used machine learning algorithms – a type of artificial intelligence – to develop a system that could determine whether any DNA found circulating in the blood was indeed shed by tumors, based on the presence of these methyl groups.

To develop the test, the team used blood plasma samples collected from individuals in China between 2007 and 2014 as part of a wider research endeavor.

The new study is not the first to report positive results for a blood test for early detection of cancer. However, the team said the research was exciting because it showed cancers could be detected before patients showed any indication of symptoms – something few studies have shown before.