A growing number of studies have stirred widespread excitement about blood tests as a means of noninvasive cancer detection with the potential for identifying personalized therapies and for assessing treatment response.
Much of the published research focuses on circulating tumor DNA (ctDNA) found in patient blood samples, with the majority concentrating on the use of “liquid biopsy” tests in relation to advanced tumor stages. Detection of early-stage malignancies, however, have proven to be more elusive.
“Several factors pose particular difficulties and challenges, including the lower frequency and volume of aberrations,” the authors of a recent review wrote, “potentially confounding phenomena such as clonal expansions of non-tumorous tissues or the accumulation of cancer-associated mutations with age, and the incomplete insight into driver alterations.”1
In fact, they continued, “as cancer is caused by a sequential series of alterations in specific cancer genes that affect the function of certain pathways and usually takes several decades to develop, the vast majority of cancers are not detected in the first 90% of the cancers’ lifetimes.”
A new form of liquid biopsy, though, appears to have overcome some of the major challenges of previous tests, offering the promise of early-stage diagnosis of multiple malignancies with a single affordable procedure.
Unlike earlier studies which focused on tumor DNA found in blood samples to detect a specific form of cancer, the test developed by researchers from Johns Hopkins University in Baltimore, Maryland, was shown to be capable of identifying eight different cancers by assessing levels of circulating proteins along with mutations in cell-free DNA.
“We applied this test, called CancerSEEK, to 1005 patients with nonmetastatic, clinically detected cancers of the ovary, liver, stomach, pancreas, esophagus, colorectum, lung, or breast. CancerSEEK tests were positive in a median of 70% of the eight cancer types,” the authors wrote.2
CancerSEEK also appears to have overcome a major concern for practitioners and patients by reducing false-positive results to a tiny fraction.
“The specificity of CancerSEEK was greater than 99%: only 7 of 812 healthy controls scored positive,” they reported. And, they clarified, they took a conservative approach in identifying the 7 instances as false positives, but the possibility exists that the test found a cancer that had not yet been detected by traditional means.
“Our study lays the conceptual and practical foundation for a single, multi-analyte blood test for cancers of many types,” the authors concluded. “We estimate the cost of the test to be less than $500, which is comparable or lower than other screening tests for single cancers, such as colonoscopy. The eight cancer types studied here account for 360,000 (60%) of the estimated cancer deaths in the United States in 2017, and their earlier detection could conceivably reduce deaths from these diseases.”