Scientists have developed a new blood test to detect cancer and locate where in the body the tumour is growing, an advance way to eliminate the need for invasive surgical procedures like biopsies.

Cancer blood tests work by screening for DNA released by dying tumour cells and detect traces of tumour DNA in the blood of cancer patients.

However, these do not indicate where the tumour resides. "Knowing the tumour's location is critical for effective early detection," said Kun Zhang, professor at the University of California-San Diego in the US.

When a tumour starts to take over a part of the body, it competes with normal cells for nutrients and space, killing them off in the process.
As normal cells die, they release their DNA into the bloodstream, and that DNA could be used to identify the affected tissue, the researchers said.

The new method screens for a particular DNA signature called CpG methylation haplotypes. Each tissue in the body can be identified by its unique signature of methylation haplotypes.

If we integrate both cancer cell and other cells signals we could actually determine the presence or absence of a tumour, and where it is growing, Zhang explained.

For the study, published in the journal Nature Genetics, the team put together a database of the complete CpG methylation patterns of 10 different normal tissues -- liver, intestine, colon, lung, brain, kidney, pancreas, spleen, stomach and blood.

They also analysed tumour samples and blood samples from cancer patients and looked for signals of the cancer markers and the tissue-specific methylation patterns.  The test works like a dual authentication process -- the combination of both signals above a statistical cutoff -- is required to assign a positive match, the researchers noted.