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NBC News doesn’t back away from shortcomings of new blood test for early cancer detection


5 Star


Blood Test Finds Cancer Before Symptoms Start

Our Review Summary

This NBC News story reports on a new approach to a blood test that might reveal early-stage cancers by detecting altered DNA floating in the bloodstream. Researchers reported an impressive success rate in finding markers that indicate cancer, although the test still needs refinement. For that reason, we think it was too early for the story to say the test can detect cancer “before symptoms start,” as so far it has mostly only been tested among people with confirmed cancer.

But the story does a good job mentioning the considerable costs of required genetic testing, and touches on potential conflicts of interest among the researchers. It outlines some of the potential risks as well as the benefits of the proposed test, and adequately explains that it is not yet ready for prime time.

One area that could have been stronger is conveying the reality that early detection does not guarantee a longer, healthier, cancer-free life, a point we raise frequently.


Why This Matters

Cancer screening (by definition, in asymptomatic patients) is complex and costly. It requires fairly complex tracking by physicians and practices, and for patients to undergo often unpleasant procedures. Because we screen for many cancers in healthy adults after a certain age, and some of those screenings require specialty involvement (colonoscopy by gastroenterology, mammogram readings by radiology) this testing adds up. A single blood test that can detect early-stage cancers (many of them at once) would be a big improvement in cancer screening. But care must be taken by journalists not to rush ahead of the science. This story kept a cautious tone.


Does the story adequately discuss the costs of the intervention?


This story gets a satisfactory in this category by including, “The genetic sequencing is also expensive right now – on the order of several thousand dollars for the 30,000 repeats the team did. But costs are coming down steadily, he said.”

Does the story adequately quantify the benefits of the treatment/test/product/procedure?


The story says, “They identified 62 percent of the patients with stage I cancer – four out of eight colon cancer patients, and 90 percent of colon cancer patients with stage II, III or IV disease. They got a positive in 45 percent of the lung cancer patients with stage I disease, 67 percent of ovarian cancer patients with stage I disease and 67 percent of breast cancer patients with stage I disease.”

This is a good start and we’ll rate it Satisfactory, but one very important thing to make clear with this type of research: It used samples where cancer was already confirmed to exist–which is different from testing only on samples where it’s not known if there is any cancer present. That could affect the accuracy.

Does the story adequately explain/quantify the harms of the intervention?


The story is dealing with a proposed new blood test for early-stage cancer, so it would require a blood draw.  While the risks of problems with that is small, the larger risk is from false positives or false negatives from the test.  The story says, “There were no false positives in 44 people who did not have cancer, they said.”  It also points our that the test didn’t detect the cancer in all cases, giving readers a reasonable expectation of risk of harms from wrong results.

Ideally the story would have included comments from a researcher not involved with the study about the sensitivity and specificity of such tests (factors that determine false-positive and false-negative rates), and how they would perform in a larger population.  The other risk here is overdiagnosis–finding cancers that don’t need to be treated.

Does the story seem to grasp the quality of the evidence?


This story does a good job of reporting the results without exaggeration.  It reports the positive results but also cautions that they need to be better before this proposed test could be used widely.  It mentions that larger trials are needed to confirm the results and improve the methodology.  It was a retrospective study of blood samples from both normal people and persons with cancer, rather than a study using animal models.

Does the story commit disease-mongering?


No disease-mongering here.

Does the story use independent sources and identify conflicts of interest?


The story does include a quote from a National Cancer Institute researcher who wasn’t part of the study team, and it also acknowledges that the lead researcher has patented the technology behind the test and is the principal of a company doing genetic screening.

Does the story compare the new approach with existing alternatives?


The story includes the following: “Several different liquid biopsies are already on the market, used to help track whether cancer treatments are working. But there’s nothing yet that can detect cancer in someone who has not yet been diagnosed.”  It also includes the following:

“Currently, colon cancer can be detected very early with colonoscopies, and even stopped before pre-cancerous growths get out of control. But colonoscopies are uncomfortable and carry a small risk of injury.

“Mammograms can detect early breast cancer, Pap smears can detect cervical cancer or pre-cancerous changes and a type of specialized chest x-ray called a spiral CT can detect lung cancer. There’s a debate over the usefulness of screening for prostate cancer but blood tests and physical exams can indicate some men at high risk.”

This is sufficient to list early methods to find cancer, but the story could have also mentioned that early screening or testing doesn’t always equate to saving lives, just more medical care. We just covered this issue as it relates to lung cancer, “Imbalanced ‘Saved by the Scan’ campaign neglects big concerns over lung cancer screening.

Does the story establish the availability of the treatment/test/product/procedure?


It’s clear that the potential use of this technology as a cancer-screening tool is some time off in the future, if its usefulness is further proven. Based on the story, readers should understand that this isn’t a tool currently available.

Does the story establish the true novelty of the approach?


The idea here is for a blood test that could detect early stage cancers, based on mutations in DNA found circulating in the blood.  That’s certainly novel enough for a story. It was also clear there are some other similar tests in development or possibly ready but not FDA approved.

Does the story appear to rely solely or largely on a news release?


There’s no indication that this story relied on a news release.

Total Score: 10 of 10 Satisfactory


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