Liquid DNA biopsies could be used for cancer screening

US researchers have developed a new blood test to detect cancer-related DNA alterations before patients experience symptoms.

The test, known as liquid biopsy, correctly identified over half of patients with early stage cancers and produced no false positives. The diagnostic accuracy of the test increased in later disease stages. 

'This is one of the first studies to use an unbiased approach - you don't know where the mutations are going to be - and to look at the blood of early-stage cancer patients to see whether we could detect alterations,' said Professor Victor Velculescu, who led the study at the Johns Hopkins Kimmel Cancer Centre, Maryland. 

The study evaluated the presence of fragments of tumour DNA (cfDNA) in the blood of 200 patients with colorectal breast, lung, and ovarian cancers compared to a control group of 44 healthy donors.

Previous studies using liquid biopsies have been used to detect cancer relapse or to determine whether treatments are working. In those cases the specific mutation in a particular patient's cancer are known, and can be targeted.

In the new study, published in Science Translational Medicine, a panel of 58 cancer-associated genes was used to screen all the blood samples with a new technology called targeted error correction sequencing (TEC-seq) which sequences the fragments of DNA 30,000 times. The test is sensitive enough to differentiate DNA modifications which normally occur from cancer driver mutations during an individual's life.

'It's actually very hard to find these mutations in the blood, especially when you don't know what the mutations are upfront,' commented Professor Velculescu. 'There are a number of confounding errors that can come up. Besides sequencing and technical errors, you can get alterations that come from the germline and can also get mutations that come from blood cells. We developed a way in which you could distinguish tumour driver mutations from these other alterations that might be in the blood.'

Next steps for the team are to increase the number of patients and type of cancers screened, and conduct clinical trials to assess the new technology impact on clinical outcomes. Such deep sequencing analyses are currently too costly to be implemented as routine diagnostic tools.