ctDNA

Detecting a disease before symptoms begin affecting your daily life can have a huge impact on outcomes. For cancer, early detection in stage I can greatly improve a patient's prognosis.

Researchers from Johns Hopkins University may have found a way to detect a variety of stage I cancers with a simple blood test. Because of advances in genome technology, researchers were able to detect little bits of tumor DNA that cancer had left behind in the bloodstream. These bits are called circulating tumor DNA (ctDNA). The researchers believe that ctDNA is a viable biomarker for cancer. For stage I cancers, 47 percent of the 640 cancer patients in a new study tested positive for ctDNA.

“That was a pleasant surprise. We were able to detect a high percent of early stage tumors, which is what actually makes early detection feasible,” said study author Nickolas Papadopoulos, Ph.D., a professor in the oncology department at Johns Hopkins.

The test becomes more accurate as the cancer progresses and tumors metastasize. For localized cancers, 55 percent of study patients tested positive. For stage 3 cancers and tumors that had ruptured, the positive results were greater than 80 percent.

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The test was most accurate at detecting breast, ovarian, and colon cancers, but many cancer types were detectable from stage I on, said study author Luis Diaz, M.D., an associate professor of oncology at Johns Hopkins.

Cancer is the second leading cause of death in the U.S., according to the Centers for Disease Control and Prevention (CDC). Using ctDNA as a potential biomarker has actually been in practice for two to three decades, although most of the work was done in the area of fetal medicine, Diaz said. “Its use as a biomarker for cancer is more recent," he said.

ctDNA monitoring is also useful for determining whether a cancer is resistant to certain treatments, according to a second study. In later cancer stages, it allowed researchers to monitor tumor progression. “It [allows] us to track the molecular changes in a tumor over time,” Diaz said.

“The pleasant idea for people was the detection of early-stage tumors that are theoretically still curable by surgery. The idea is that if you detect that, you can theoretically save the patient,” says Papadopoulos. Right now there are no existing detection tests for early stage cancers, he said.

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One benefit of ctDNA testing is ease of use. All it takes is an extra vial of blood drawn during an annual checkup or other blood test. However, accuracy at this stage increases with a larger biological sample. The more blood, the bigger the pool of cells—which means more ctDNA to detect.

Increasing the sensitivity of the test is one of the next steps for researchers, as well as looking at different biological samples, such as urine and saliva, for ctDNA evidence. Stool samples are already used to detect colon cancer, Papadopoulos said. But he sees major benefits to a blood test.

“The good thing with the [blood] plasma is that you can detect a lot of different tumor types in the same material,” Papadopoulos said.

Early-stage detection of cancer is just one of the many potential benefits of investigating the human genome. “We witnessed a revolution in the last few years in genomics,” Papadopoulos said. 

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