The Ugly Side of Cancer Screening
In clinical practice, the goal of cancer screening is ultimately to reduce mortality. A researcher from the Brigham’s Center for Surgery and Public Health, however, questions the assumption that more screening is necessary and always better. In a Viewpoint piece published in the Journal of the American Medical Association, Dr. H. Gilbert Welch details the prevalence of overdiagnosis in cancer screening and writes about whether an early diagnosis is truly beneficial. Dr. Welch told us more about his area of research:
Q: You describe cancer screening as “counterintuitive.” What are some of the common misconceptions about screening that do not align with patient outcomes?
A: The most common misconception is that cancer screening “can only help,” which is simply not true.?Screening results in false alarms, more testing, and treatment for cancers that would otherwise never have caused problems.?Screening is also known to make people feel more anxious and less healthy.?It can also lead to procedures and treatments that produce physical harm — even death (albeit rarely) — and it makes people poorer: All this costs money, money that increasingly comes out of patient’s pockets.?
There is also the misconception that screening is tremendously beneficial which, again, is not true.?If it helps at all, it helps a little.?Even our best screening tests have a relatively small effect on cancer mortality: in the general population, roughly 1,000 must be screened for 10 years to avert one cancer death.?Cancer treatment, on the other hand, does help a lot.?And, ironically, the better we can treat cancer, the less important screening becomes.?
These misconceptions are not the fault of patients; they are the fault of the health care system. Cancer screening is aggressively promoted as “saving lives.” Screening produces numerous cancer “survivors,” and therefore, it is easy to conclude that these individuals have benefited from the test.?However, there is another possibility: They were diagnosed and treated for a cancer that was otherwise not destined to cause any problems.??
Q: What is the barnyard pen analogy and how does it relate to cancer screening?
A: The goal of cancer screening is to catch cancers early – in this analogy, to catch them before they get out of the barnyard.?However, not all cancers have the same biology, behavior, and propensity to grow.?Let us consider birds, rabbits, and turtles. The birds have already escaped the barnyard: they are the fastest growing and most aggressive cancers, those that have already spread by the time they are detectable. Screening can’t help with the birds; the question is whether treatment can.?The rabbits are more slowly progressive cancers, and they can be caught early.?They are the cancers that screening can potentially help with.?And then there are the turtles: there’s no need catch them, because they’re not going anywhere anyway.?
This analogy has been around for more than half a century. It highlights two hidden assumptions of screening. First, all bad cancers can be found early, and second, all cancers found early are destined to become bad.?The birds explain the limited benefit of screening; the turtles explain its major harm —overdiagnosis.?
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Q: What are the harms of overdiagnosis?
A: No one wants to be diagnosed with cancer needlessly.?Just the word has a way of making one feel anxious and vulnerable.?However, the bigger harm is that patients and providers feel compelled to initiate cancer treatment – treatment that cannot help, because there is nothing to fix.??
Q: What do you hope to see change in the future regarding cancer screening?
A: I hope to see less aggressive treatment for people whose cancers are detected by screening (as well as those cancers we doctors stumble upon while investigating other problems).?This is thankfully already beginning to happen.?Small cancers of the thyroid, prostate and kidney are now sometimes being simply watched and only treated if they are obviously growing.?
But I’d also like to see us find fewer cancers in the first place.?While prompt diagnosis and treatment of patients with symptoms of cancer is very important, I believe widespread screening in asymptomatic people has created as many problems as it has solved.?I realize this is a minority view. At the very least, I hope to help people understand why the best screening test is not the one that finds the most cancer.?That’s a recipe for overdiagnosis.?The best test is the test that finds the few people with cancers that screening can help, without subjecting many others to needless alarms, additional testing, and unnecessary treatment.?
To read H. Gilbert Welch’s full paper, visit: