Blood Test Shows “Tremendous Promise” For Detecting Cancer Early
The ultimate goal is to get to a day where a simple blood test can detect a small tumour growing in your body, giving doctors time to cure you before its too late.
Well, it would seem a team of scientists has taken us one step closer to that goal, writes Science. Based at GRAIL, a biotechnology company in Menlo Park, California, the team revealed their progress at the annual meeting of the American Association for Cancer Research. Using full-genome sequencing to analyze DNA shed into the blood by dying tumour cells, they noticed evidence of cancer in 65% of a group of patients already known to have early disease.
The results are noticeably similar to those published recently by other research teams. Together, both show “tremendous promise” for detecting cancer early using liquid biopsies, explained cancer researcher Daniel Haber of Massachusetts General Hospital in Boston, who was not involved with the work.
Despite there being several companies and academic labs working on this new form of cancer detection, GRAIL has turned heads specifically because of the large amount of money it has raised. In order to build a reference set of what to look for in its blood test, GRAIL is cataloging cancer-related mutations in cell-free DNA in the blood of people with 20 types of cancer and others who are apparently cancer-free. So far, the study has enrolled more than 10,000 people so far.
With blood samples totaling 878 people, with newly diagnosed cancer and 580 people without the disease, GRAIL went ahead and performed three different kinds of assays that analysed DNA across the entire genome. One, in particular, looked for mutations in about 500 known cancer genes, a second detected abnormal numbers of copies of genes, and the third analysed patterns of methylation, which are chemical tags on DNA that turn genes off or on. In addition, the company looked for mutations that pop up in the white blood cells of healthy aging people and removed them from the analysis to leave only cancer-specific patterns.
The team later looked at how well each assay’s data would have predicted cancer in the patients. For 196 people with five highly lethal cancers that are difficult to detect early – pancreatic, lung, ovarian, liver, and esophageal – the methylation test did best, indicating cancer in 65% of those whose cancer at the time of their blood sample had not spread detectably to other organs, besides lymph nodes. As expected, the detection rate was higher – 95% – for metastatic cancers because these patients’ tumours are larger, can be in multiple organs, and release more DNA into the blood.
Despite the fact that the 65% sensitivity rate for non-metastatic cancer needs to be confirmed in another set of people, it is on par with some other tests, such as one published recently from a group at Johns Hopkins University in Baltimore, Maryland, that sequenced a small set of genes and combined the results with measurements of several cancer-linked proteins in the blood.
Also, the false positive rate for all three GRAIL tests was very low; only five of the 580 people in the group considered cancer-free tested positive. Two people with a false positive later turned out to have ovarian and endometrial cancer, suggesting the false positive rate could be even lower, explained Alex Aravanis, head of R&D.
Being able to detect a possible tumour from a blood test is just the first step, going forward we would hope that any liquid biopsy would point to the organ that is the source of the cancer so that oncologists could use imaging to confirm any tumour and remove it before it has spread. The Hopkins group was able to successfully locate the tissue origin in many cases using its protein biomarkers. GRAIL hinted that it has data indicating which tissue the tumour DNA is coming from but isn’t yet ready to release those results. Blood Test