Can This Blood Test Really Detect Cancer Years Before Symptoms Show Up?
In a new paper, researchers show promising results about an early cancer screening blood test.
Unlike Theranos and its "single drop of blood" claims, this real test uses a vial of blood to test for genetic evidence.
The researchers emphasize this is a first step that must be studied in depth to fine-tune and explore it.
Chinese scientists say a new blood test can detect five kinds of cancer up to four years before a doctor could. For members of the public still wary in the wake of Theranos, the tech company that fraudulently purported to run a litany of health tests using just a single drop of blood, how is this test different, and what might it accomplish?
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In a new paper in Nature Communications, the scientists introduce a new blood testing system they’ve named PanSeer, which puts together existing technologies for many different genome tests. From the paper:
“We defined a set of differentially methylated CpG sites using publicly available microarray and Whole Genome Bisulfite Sequencing data from The Cancer Genome Atlas and genomic regions known to be cancer-related in the literature, as well as internal Reduced Representation Bisulfite Sequencing data from a variety of cancer tissues. From these sources, we compiled a targeted panel of 595 genomic regions for further interrogation in plasma samples.”
The team then began accumulating data from well over 100,000 people. Residents in the researchers’ local Taizhou area, which is a designated area that includes the large city of Taizhou in a county-like setup, entered into a long-term combination of regular blood draws and regular screenings for the five most common cancers in Taizhou.
“As part of the study, 123,115 healthy subjects aged 25 to 90 years provided blood samples for long-term storage from 2007 to 2014; these individuals were then indefinitely monitored for cancer occurrence through linkages with local cancer registries and health insurance databases. By the end of 2017, a total of 575 initially healthy subjects (who presented as asymptomatic) were diagnosed with one of five common cancer types (stomach, esophagus, colorectum, lung or liver) within 4 years of initial blood draw.”
From there, the scientists studied the genetic material in the blood samples. They looked for evidence that the telltale places they analyzed showed DNA methylation, a chemical process in which the DNA is altered. That can be adding, erasing, or a chemical form of “noticing” where a marker indicates where a gene has changed. All of this has detectable ripples in the samples.
“The PanSeer assay was solely developed to detect cancer regardless of the tissue-of-origin by targeting a limited number of genomic regions that are commonly aberrantly methylated across different cancer types, allowing it to be used as a potential first-line inexpensive cancer screen,” the researchers explain. “It also requires a comparatively small amount of input DNA (from only a single tube of blood).”
An “assay” is the technical term for a test like this, where scientists identify and measure quantities of specific components. Drug tests and COVID-19 tests use their own assays. The PanSeer assay is very new and strictly in the exploration phase, the researchers emphasize. It has promising results and limitations that must be explored in the future. Just being able to identify the presence of genetic markers isn’t the same as ensuring better outcomes for patients, and this research makes that clear as part of a suggested roadmap for what’s next.
Over-treatment of early breast cancers and prostate cancers has subjected patients to what some have said is undue suffering for certain slow-growing cancers that might not even have shortened their lives. So the scientists are thoughtful and pragmatic. They conclude:
“In the future, to fully establish the clinical utility of PanSeer and fully validate the results of pre-diagnostic detection of cancer, we hope to proceed with a large prospective study of healthy individuals to determine if non-invasive cancer screening can reduce cancer deaths in a cost-effective manner.”
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