Thu 12 Nov 2015
“Liquid biopsies” is a new buzzword in medical circles at the moment.
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Over the last few years it has been shown that circulating tumour cells (CTC) and cell-free circulating tumour DNA (ctDNA) can be found in the blood of many but not all patients with cancer. As DNA sequencing technology has become cheaper and faster it has become possible to isolate this DNA from blood samples and sequence it to look for mutations in that DNA that are associated with both the presence of cancer and sometimes the presence of mutations associated with susceptibility or resistance to particular types of cancer treatments.
More studies are being published showing that detecting this DNA in the blood has the potential to guide cancer treatment. Obviously from the patient’s point of view it is a lot simpler and easier to have a blood sample taken than to have a piece of tissue taken from somewhere within their body to get samples of tumour cells.
Many companies are competing with each other and spending millions of dollars to bring these types of tests to the market because by some estimates the market could grow to be worth 40 billion dollars a year. However the technology is far from being proven to be clinically useful at present. There are as yet no studies showing that using liquid biopsies can result in improved cancer outcomes in real cancer care situations. Dr Nick Turner of Britain's Institute of Cancer Research said the technology had huge potential but more evidence was still needed. "What is really missing at the moment is the hard evidence that using liquid biopsy and treating patients on that basis improves hard endpoints like how long the patient lives. The field really needs those studies to change practice," he said.
One of the problems with the current technology is that ctDNA can’t be detected in all patients with cancer. ctDNA was detectable in 82% of patients with solid tumours outside the brain, but in only 50% of patients with medulloblastomas or metastatic cancers of the kidney, prostate or thyroid, and in less than 10% of patients with gliomas. In patients with localized cancer of all the types evaluated, only 55% had detectable ctDNA.
For the companies seeking to bring the liquid biopsy technology to market as a cancer screening method the situation is even worse as there is no evidence at all that the technology will be useful, no published data on what proportion of hidden early cancers will be detected and potential for it to be harmful to both individuals and healthcare budgets.
It is likely to three to five years before we know if and in which situations this technology will be clinically useful.
Medscape (requires registration to access): http://www.medscape.com/viewarticle/853942?nlid=91223_1024&src=wnl_edit_medp_path&uac=136548BV&spon=43&impID=884819&faf=1
Laboratory News: http://www.labnews.co.uk/news/liquid-biopsy-to-track-lung-cancer-18-06-2014/
MIT Technology Review: http://www.technologyreview.com/featuredstory/534991/liquid-biopsy/
Science Based Medicine: https://www.sciencebasedmedicine.org/liquid-biopsies-for-cancer-life-saving-tests-or-overdiagnosis-and-overtreatment-taken-to-a-new-level/
Annals of Translational Medicine: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4356857/
Science and Translational Medicine: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4017867/