13 March 2017
ByAppeared in BioNews 892
Researchers have developed a new blood test that can not only detect cancer at an early stage, but can also indicate where the tumour is located in the body.
So-called 'liquid biopsies' detect fragments of tumour DNA called cell-free DNA (cfDNA), but until now they have only been able to detect the presence or absence of a tumour.
Professor Kun Zhang of the University of California, San Diego, and colleagues found that normal cells that compete with cancer cells for nutrients and space also release their DNA in the bloodstream. This DNA leaves organ-specific signatures – known as CpG methylation haplotypes – that could help doctors determine which part of the body has been invaded with cancer.
'We made this discovery by accident. Initially, we were taking the conventional approach and just looking for cancer cell signals and trying to find out where they were coming from. But we were also seeing signals from other cells and realised that if we integrate both sets of signals together, we could actually determine the presence or absence of a tumour, and where the tumour is growing,' Professor Zhang said.
The researchers generated a comprehensive database of tissue-specific signatures for ten different tissues (liver, intestine, colon, lung, brain, kidney, pancreas, spleen, stomach and blood). They then compared 29 patients with lung cancer, and 30 with colorectal cancer, with 75 healthy individuals to see whether they could distinguish cancer patients from healthy controls – and identify the where tumour was originating from.
As they report in Nature Genetics, they were 83 percent accurate in identifying the correct tissue of origin in the colorectal cancer samples, and 92 percent accurate in identifying lung-cancer samples.
'Current [liquid biopsy] assays are mainly applicable to people who have already been diagnosed with cancer, so you already know where the cancer comes from. But to go to the holy grail of early detection you need to know tissue origin,' said Professor Zhang.
Professor Yuval Dor of the Hadassah Medical School in Israel, who also works on DNA methylation signatures, said that 'the clinical potential is enormous, for detection of cancer and much beyond'.
The scientists are now aiming to commercialise the blood test through the genetics startup Singlera Genomics.