Clinicians and researchers agree that it's best to treat cancer as soon as possible, which means an early diagnosis can benefit many people. DNA that has broken away from cancer cells and can be detected in the bloodstream, called ctDNA (circulating tumor DNA), has presented a new way to diagnose cancer; ctDNA is a type of cell free DNA. The ctDNA can be detected at very small amounts, and could identify cancers earlier than other diagnostic methods.
A company called GRAIL LLC created a blood test called Galleri, which is meant to diagnose 50 different kinds of cancers with only one blood draw.
A trial of this test has now been conducted. It evaluated 6,238 adults who had been referred for urgent diagnostic procedures such as endoscopies or imaging to determine whether they had lung, gynecological, lower gastrointestinal (GI) or upper GI cancers. Many study participants had presented with symptoms such as unexpected weight loss, changes in bowel habits, rectal bleeding, pain, or anemia, for example.
The study determined that the test can correctly identify two out of three cancers, and was able to reveal the primary site of the cancer in 85 percent of cases.
In this previously reported method, the researchers isolated DNA from blood samples that had been provided by the volunteers. This cell free DNA that has been collected is treated and mixed with specific probes that have known sequences of interest. These probes bind to their target sequences (known from previous work) in the cell free DNA from the patient, and the ctDNA is extracted. Then the researchers can analyze these sequences, and the methylation characteristics of the targeted ctDNA is assessed as cancerous or non-cancerous.
There were 323 people who got a positive diagnosis from the GRAIL test, and of those individuals, cancer was confirmed in 244 of them. The assay therefore had a positive predictive value of 75.5 percent, a negative predictive value of 97.6 percent, and specificity of 98.4 percent, which are all great indicators that the test is working well.
The most common types of cancers found in the study volunteers were colorectal (found in 37.2 percent of patients), and lung (22 percent). This test can be used to quickly identify people who need additional cancer screening.
"Earlier cancer detection and subsequent intervention has the potential to greatly improve patient outcomes. Most patients diagnosed with cancer first see a primary care physician for the investigation of symptoms suggestive of cancer, like weight loss, anemia, or abdominal pain, which can be complex as there are multiple potential causes. New tools that can both expedite cancer diagnosis and potentially avoid invasive and costly investigations are needed to more accurately triage patients who present with non-specific cancer symptoms," said co-lead study investigator Brian D. Nicholson, Associate Professor at Oxford University's Nuffield Department of Primary Care Health Sciences.
"These exciting results will inform our development of an optimized classifier for use in symptomatic patients with a suspicion of cancer," said Sir Harpal Kumar, president of GRAIL Europe.
Sources: Annals of Oncology, University of Oxford