By the time a person notices the first symptoms of cancer, the disease has often spread too far to be treated successfully. But that could change, thanks to a blood test that can detect more than 50 types of cancer, often at an early stage.

Michael Seiden at US Oncology Research in The Woodlands, Texas, and his colleagues analysed blood samples from 2,185 people with cancer and 2,131 healthy individuals. The researchers scoured the samples for DNA that had entered the bloodstream on cell death and probed the DNA for chemical alterations that are indicators of cancer.

The authors then developed an algorithm to predict the presence of cancer on the basis of these chemical fingerprints. For a group of 12 particularly deadly cancers, such as pancreatic cancer, the algorithm could detect tumour signatures in 39% of people with early-stage cancer and 92% of individuals with advanced cancer. In 93% of cases, the test could also predict the tissue in which the cancer had originated.

The ability to detect multiple types of cancer and identify a cancer’s location in the body could make successful treatment more likely, the authors say.