A blood test which can detect five of the deadliest cancers is being developed by scientists.
When colon, lung, breast, stomach and endometrial cancer is present, a "striking" chemical modification of DNA occurs, said researchers from the National Human Genome Research Institute (NHGRI) in the US.
They found that when cancer is present, there are higher amounts of methylation which decreases a gene's activity "like a dimmer on a light switch".
They are hoping to use their discovery to develop a blood test to diagnose a variety of cancers at early stages, when treatments can be most effective.
Dr Laura Elnitski, a computational biologist at the NHGRI said: "We were so excited when we found this candidate biomarker. It's the first of its kind to apply to so many types of cancer.
"We have laid the groundwork for developing a diagnostic test, which offers the hope of catching cancer earlier and dramatically improving the survival rate of people with many types of cancer."
Current blood tests are tumour-specific, which means clinicians must find the tumour first and test a sample, but the new approach requires no prior knowledge that cancer is present.
It would be less intrusive than other screening approaches such as colonoscopies and mammograms, and could be used to screen high-risk individuals or monitor tumour activity during treatment.