This story is about one of several studies on so-called “liquid biopsies” that were presented at the 2018 annual conference of the American Society of Clinical Oncology (ASCO). Liquid biopsies are blood tests for possible markers of cancer in the blood. It’s an emerging technology (we have written about extensively) that has yet to be shown to be as clinically usefully as the current gold standard for confirming a cancer diagnosis: getting a tissue sample.
The Guardian story not only misleads readers with a grandiose headline, it fails to provide readers with a balanced discussion of the significant limitations and harms that many experts consider salient when it comes to liquid biopsies. The cost and availability of these specialized tests are neglected, as is the fact that the study mentioned has yet to be published.
What would have helped this article most of all would have been including an additional independent, critical voice that could speak to these likely reader concerns: Is this technology ready for widespread use? Is it as good or better as existing cancer screening methods? Who should get this test?
When articles are written as this one is — with unjustified speculation suggesting that a simple test will catch cancer early and that means less people will die of cancer — it does a huge disservice to readers. It is speculation bordering on misguided promotion.
The appeal of a noninvasive test for cancer is undeniable, but at this time the consensus opinion of cancer specialists is that this technology is not ready for meaningful clinical application because the accuracy, reliability, and reproducibility are still unknown. Any article on liquid biopsies should make that clear.
In other words, though there is great appeal from such a test, here described as a “holy grail,”, it isn’t clear how far along we are to seeing such tests in clinical practice. The first place they may appear could be for a different indication – specifically, following patients diagnosed with cancer who undergo treatment. Such tests could be used to determine if there is microscopic residual cancer not seen or identified using current methods. The goal described in the Guardian story is more challenging.
Costs are not mentioned.
As we’ve reported in the past, one company has marketed their similar test with a $1,000 price point.
This story errs on the side of promoting potential benefits without providing critical context.
It includes two reckless quotes (one by a lead author, another by an independent source) which suggest that the liquid biopsy:
This study did not address cure, survival, or productivity.
Furthermore, the story lists the accuracy of “diagnosing” 10 different types of cancer (with an ‘accuracy’ of 56% – 90% depending on the cancer) without making it clear these are the percentage of people already known to have cancer who had a positive test confirm its presence.
We did appreciate this inclusion:
The number of patients in who cancers were detected was small. For example, although the test detected ovarian cancer with 90% accuracy, only 10 ovarian cancers in total were detected.
To be useful to readers, the story should have included the rate of false-positives and false-negative results. Or, what’s known as test sensitivity — how often the test is correct when the disease is present; and specificity – how often the disease tests negative when the disease is not present. The percentages reported likely represent the sensitivity. So the article did provide some numbers, but it was limited and not explained in a way that would allow the reader to appreciate how good (or not good) the test really was.
The story includes no mention of what many experts consider to be the most important considerations when it comes balancing the harms vs. benefits of liquid biopsies. These include:
The story includes some basic details about the trial. But it didn’t discuss limitations–notably that any data presented at a medical conference is preliminary until published and peer-reviewed.
Also, the story touts potential benefits for screening healthy-seeming people for early signs of disease. But in the study itself, about half of the people had already been diagnosed with cancer. If the test is applied to the general population as this story suggests is appropriate, there will likely be many more false-positives than were recorded in the study.
It’s also important to note that an expert panel from ASCO and CAP (American Society of Clinical Oncology; and College of American Pathologists) recently reported:
While it offers overly inflated claims of benefit, there is nothing to suggest that the piece displayed disease mongering about cancer itself. The story would have been stronger, however, if it had noted that catching cancer earlier doesn’t always translate to curing cancer.
The story didn’t disclose that the researchers had significant conflicts of interest. (See disclosures.)
The current gold standard for confirming the diagnosis of most cancers is a tissue sample. This is not addressed in the article and should have been. It also could have been clearer that for some cancers there are no approved screening tests.
Availability of liquid biopsies are not directly addressed, though it is implied they are not yet available. We’ll give this one a just-barely satisfactory.
There are a host of different liquid biopsies being tested. They look for a variety of markers associated with cancers such as proteins, cancer cells, and even circulating tumor DNA (ctDNA) is in the case of this study.
This was not mentioned in the article.
We couldn’t find a related news release. Because the story includes quotes from people not affiliated with the study, we think it’s safe to assume the story didn’t rely on one.