An experimental blood test could one day make early detection of cancer possible. At least two research studies published this year show exciting advances in DNA methylation analysis, a method that examines biochemical alterations of genetic material for the presence of cancer.
Dubbed “liquid biopsies” by some, one of the experiments accurately predicted the emergence of 50 cancers and where the tumor was growing in thousands of people, reports Chemistry World; the other made predictions up to four years before symptoms occurred, according to Scientific American. The existence of a single test that can potentially screen for multiple cancers at once could lead to early interventions and treatments that save lives.
“Achieving this goal is one of the most ambitious undertakings in healthcare, and this is exactly what we are committed to doing,” team scientists from the California-based healthcare company, GRAIL, wrote in a feature for Nature Research.
Early Detection of Cancer
Anyone who visits their primary care physician on an annual basis knows that a handful of cancer screening tests already exist. Mammograms, for instance, look for early signs of breast cancer, colonoscopies check for colon cancer and Pap tests screen for cervical cancer. Undergoing such tests before symptoms appear can make a difference. More than 90% of women diagnosed with breast cancer in the early stage survive at least five years compared with women diagnosed at late stages, reports Cancer Research UK. More than nine in 10 patients with bowel cancer will survive at least five years if diagnosed early and 90% of women diagnosed early for ovarian cancer will survive at least five years compared to those diagnosed when the disease had advanced to a late stage.
Unfortunately, cancer screening tests return an unacceptably high rate of false positives. A study published in Cancer, a peer-reviewed publication from the American Cancer Society, showed that over a period of 10 years, about 50 to 60 of 100 women who get annual mammograms; 23 of 100 people who get stool tests; and 10 to 12 in 100 men screened for prostate cancer have false-positive results.
Even tests that return low false-positive results depend on the presence of malignant cells or tumors. For instance, mammograms depend on anomalies in breast tissue. Colonoscopies are accomplished using a long, flexible, tubular instrument that transmits an image of the colon to a monitor, where a doctor examines the tissue for abnormalities. And a Pap test involves sampling a small amount of mucous from the cervix and analyzing it under a microscope to detect abnormal cells.
Exciting new approaches could provide accurate and early detection of cancer long before abnormal tissue or cells appear.
DNA Methylation Analysis
Early cancer detection could be possible because of a biochemical process, called methylation, which is the transfer of four atoms — one carbon atom and three hydrogen atoms (CH3) – from one substance to another. The transfer to and from substances work as a kind of biological switch, turning on and off a host of systems in the body. In the case of DNA, methylation can turn on or off the expression of certain genes linked to cancer. Because this process occurs in tens of millions of known places in the body, it offers a global view of cancer, the GRAIL researchers say.
“In contrast to typical cancer mutations that only affect a handful of genomic locations, there are nearly 30 million sites, known as CpG sites, across the human genome that can be methylated or unmethylated, making them a ubiquitous and rich signal for detecting cancer,” the GRAIL team writes in Nature Research.
GRAIL scientists and those from the second team that published their research in Nature Communications, studied blood from tens of thousands of people over a period of years. The scientists looked at methylation patterns in the DNA of the blood and plugged the information into machine learning algorithms. Over time, some of those people developed cancer and that information was also fed to the algorithms. Eventually, the machine learning algorithms began to recognize a relationship between abnormal methylation patterns in the DNA and certain cancers. Next, the scientists sampled blood from new patients and fed information about methylation patterns in that blood to the machine learning algorithms, which were able to make predictions from what it saw.
“What we showed is: up to four years before these people walk into the hospital, there are already signatures in their blood that show they have cancer,” Kun Zhang, a bioengineer at the University of California, San Diego, and a co-author of one of the studies told Scientific American.
Although more research is needed, DNA methylation analysis could fundamentally change cancer treatment. For a disease that is the second leading cause of death worldwide, the progress marks one of the most exciting possibilities in the early detection of cancer.
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