With the exception of a misleading and somewhat hyped headline, this British newspaper story fairly describes results of some data-mining research that adds strength to previously observed associations between a form of seriously elevated blood platelet levels (thrombocytosis) and some types of cancer.
Researchers at the University of Exeter claim its findings are solid enough to help general practitioners use commonly done blood tests that happen to include platelet counts as clues to earlier diagnosis of unsuspected cancer in adults patients — clues akin to a woman finding a breast lump that needs a biopsy — while also making clear that such patients would need “further investigation.”
The headline “High Blood Platelet Count ‘As Good A Cancer Predictor as a Lump in the Breast” is unfortunate because it suggests to the reader that the blood test is a test for breast cancer (it isn’t a test for any specific cancer or any cancer period) and infers that most breast lumps are cancerous (the vast majority are not). We also wished the story’s appropriate cautions and caveats about the use of platelet counts clinically were included much higher up in the text. But, to its credit, the story used quotes from third parties to make clear that more research is needed to confirm the new findings, that routine platelet testing is not what’s called for here, and that elevated platelet levels are potential markers but not at all proof of the presence of cancer.
In general — albeit with caveats — the earlier cancers are diagnosed the more likely treatments are to be appropriate and effective. But early detection remains a challenge for scientific reasons but also for reasons related to costs of care, access to care, and issues related to unnecessary imaging and biopsies. Thus the notion that elevated platelet counts — made evident in the results of a simple blood test — are a reliable marker of significant numbers of early, unsuspected cancers of the esophagus, stomach,lung, uterus, prostate, breast or other organs is tantalizing, but in great need of context. For one thing, thrombocytosis can be due to infections, anemia, inherited blood disorders and other conditions that have nothing to do with cancer. For another, platelet counts can vary widely over time and with age within the same patient if there is inflammation or infection, for example. And for a third, further testing of those with elevated platelet counts to rule cancer in or out is not always safe, effective, or useful.
Blood testing costs vary widely, but can run to hundreds of dollars, even for those covered by national or private health insurance. Moreover, there are likely even heavier costs associated with follow up cancer screenings and tests for those considered at risk because of thrombocytosis. The article makes no mention of potential or actual costs, and one suspects that a quote from a UK health information officer may have had costs in mind when she said “measuring platelet count in patients who don’t otherwise warrant a blood test is not necessarily a good idea. But if a patient has a blood test for another reason and a high platelet count is found, then one of the possible diagnoses doctors should consider is cancer.”
The story’s author did a good job of describing the numbers of patients whose data were drawn from a national database, and the percentages across ages and genders who were identified with some form of cancer within a year of a high platelet count, compared to percentages of who were not diagnosed with cancer. It also noted the rate of cancer diagnosis in the general population overall as a comparative factor. There were also data given about the types of cancer most diagnosed and the potential impact for early diagnosis. The thoughtful reader will come away with the notion that even if platelet counts are utilized widely, they are not going to serve as markers for most cancers that arise in adults.
One thing the story needed on this note was better framing on how these results differed by age. Our concern is there may be unnecessary anxiety for some people to pressure their doctor into performing a platelet count beginning at a young age that may not be necessary.
The story should have stated more explicitly the significant potential downsides (clinical and financial) of mass use of primary thrombocytosis screening, and even the harm that can potentially occur when an “incidental” finding of elevated platelet levels must be further investigated in the absence of other cancer risk factors or symptoms. It could raise anxiety levels of people who may have elevated platelet counts due to other reasons or younger people feeling they need to be tested because the results by age weren’t mentioned.
The article clearly explained where the data originated, how the study was done, and (with the use of quotes) some of the limitations of the findings.
We do think there was a limitation worth noting, though. Usually when you conduct a matched case-control study, you have the same number of controls per cases or more controls matched per case (which strengthens the power to detect differences). The lack of controls in this study may have produced inflated results.
No mongering here. They didn’t try to overplay thrombocytosis as a cancer predictor.
The story used information and quotes from those not associated with the study, and we detected no conflicts of interest.
There are no relevant alternatives to discuss.
They did mention blood tests being ordered by GP’s making assumptions that it is widely available.
The story did a good job of pointing out previous research suggesting associations between cancer and thrombocytosis, and how the new study strengthened those associations.
The University of Exeter published a news release on its website, from which the story drew substantially. But the story also used outside sources.
Systematic, Criteria-Driven
Monday at #ADA2021, an infectious disease epidemiologist, a journalist, and a researcher shared perspectives on communication of risk in the era of COVID-19: http://ow.ly/ROfR30rMeE7 @AstleyCM @garyschwitzer @berthahidalgo @ADA_DiabetesPro
Shoutouts to @susan_bewley @drkevinknopf @MichaelBaum11 in this call for more than fawning coverage from press releases for these kinds of stories.
Also, linked history inside goes back 5 years just on Grail apparently trying to become Holy Grail. https://twitter.com/garyschwitzer/status/1408849696416841731
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