Scientists inch closer to blood test to detect early stage cancer

Scientists are edging closer to developing blood tests that could detect early stage cancer, before patients show any symptoms of the disease.

One such test, called PanSeer, can potentially spot five types of cancers up to four years earlier than current diagnostic methods, according to a study published Tuesday in the journal Nature Communications.

The test works by detecting tiny bits of DNA that tumor cells release into the bloodstream. Researchers have been working on this type of DNA sequencing application for years, and the development brings the industry a step closer to using a blood test to diagnose cancer before it progresses into advanced stages, which are more difficult to treat.

“We’re turning the proof of concept stage into a commercial product that is robust, inexpensive and can be deployed in clinics,” said study co-author Kun Zhang, department chair of bioengineering at the University of California, San Diego, who co-founded Singlera Genomics, the company that designed PanSeer. At this point, however, the test is still years away from being used by doctors.

Dr. Eric Klein, a urologist at the Taussig Cancer Institute at Cleveland Clinic, called the findings “another validation, adding to the several other studies that have been published, that cancers do release bits of DNA into the bloodstream that can be detected at low levels.”

“The four-year prediction was incredible,” Klein, who was not involved with the research, added.

In the study, Zhang and his team retroactively analyzed blood samples taken from 605 asymptomatic people, 191 of whom were later diagnosed with colorectal, esophageal, liver, lung or stomach cancer using standard diagnostic methods, to see if they could detect the tiny fragments of DNA that would indicate cancer.

The researchers also tested PanSeer’s accuracy on plasma samples taken from 223 cancer patients, as well as 200 tumor and healthy tissue samples. They determined that the test could detect cancer DNA in the blood of asymptomatic patients with 95 percent sensitivity, spotting signs of cancer as much as four years earlier than current screening methods typically would. (The higher the sensitivity, the lower the likelihood of false negatives.)

However, the test is unable to distinguish which of the five types of cancer a patient has, based on the DNA fragments, meaning additional tests would be needed to determine the specific cancer type.

Zhang believes the technology is one clinical trial away from being approved for use in patients, but that means that a blood test that detects early stage cancer is still years away from being used in doctors’ offices. Even when it is, the tests likely will not replace current screening methods for certain cancers, including mammograms, colonoscopies and Pap tests, anytime soon.

“At least initially, blood tests will not displace the need for routine screening tests that are currently recommended by physicians. They may eventually surpass current tests, but not right away,” Klein said. “We also have to be careful that patients do not think that because they have had a negative test, that they have zero risk for cancer.”

Where the tests could be particularly useful is in diagnosing certain types of cancer that are currently difficult to screen for, including stomach and liver cancer.

“Every screening tool that has been applied to these cancers hasn’t been very effective, and that is where this could be really useful,” Dr. Mark Roschewski, clinical director of the Lymphoid Malignancies Branch of the Center for Cancer Research at the National Cancer Institute, told NBC News.

According to Roschewski, being able to create a test that produces 100 percent specificity — meaning no false positives — rather than the PanSeer’s 96 percent, is an important trait that any cancer blood test that hits the market should provide.

“People without disease need to test negative,” he said. “The last thing you want to do is take someone who is completely healthy and put them through a series of tests and the stress of being told they have cancer when they don’t.”

Roschewski also warned that just because cancer is detected at a very early stage, it may not necessarily be able to be treated at the time of diagnosis, while other slow-growing types of cancer may not require treatment for years.

Klein noted that it’s also important for patients to understand that PanSeer and its competitors are first generation tests that will not always detect every type of cancer the tools are said to detect.

“But this is validation that the approach has real substance and, as the understanding of the technology advances, we will make a real dent in cancer mortality using this approach,” Klein said. “It’s fundamentally different technology, and a different way of searching for cancer than we’ve ever had in the past.”

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