In the western world, we have been trained to participate in all kinds of health screening because we are told that hidden dangers lurk inside us. North Americans are remarkably enthusiastic about screening. As a result, it is a multi-billion-dollar industry.
Conventional wisdom is simple: finding disease early saves lives by catching small problems before they become big ones. But early diagnosis can have both good and bad consequences. While it can help some people – as is true across all of medicine – it always carries the danger of over-detection: identifying abnormalities that are not destined to bother us.
When it comes to cancer, over-detection has especially significant consequences because it often labels healthy people as “cancer patients.” With that label comes large amounts of anxiety, unnecessary treatment, potential harm without benefit, and diversion of healthcare resources away from patients who truly need care. The intentions behind cancer-screening programs are good, but for more than a decade the evidence has not matched the hype.
Almost everyone knows someone who has or has had cancer. My mother died of it. So did her father and brother. A friend from university recently received a cancer diagnosis. This pattern surely mirrors the experience of many.
We are all scared of cancer. It has a reputation – well deserved in some instances – of being a horrible disease. Part of your own body has gone hopelessly awry, growing uncontrollably, and spreading in mysterious and unpredictable ways. At its worst, cancer weakens and kills a person.
We go to great lengths to avoid facing the big C.
There are two main strategies for reducing the impact of cancer. The first is health promotion – encouraging behaviours such as regular exercise, a balanced diet, avoiding smoking, and limiting sun exposure. The second is early detection – using tests to find cancer before symptoms appear. (Although screening does not prevent cancer per se, it does aim to catch it early enough to intervene.)
Early detection has strong appeal. It offers a concrete medical service and a tidy answer: either you have something, or you do not. For healthcare professionals, it carries additional advantages: tests are quick to order, they keep appointments brief, fit smoothly into billing systems, and they are widely assumed to prevent the higher costs of treating advanced disease.
Over time, healthcare systems have been remarkably successful at promoting the idea that early intervention is better.
As a result, we screen for cancer – a lot. We test our breasts, colons, cervixes, and prostates according to standardized (sometimes shifting) guidelines. Public health campaigns often launch before strong evidence exists, then distil complex tradeoffs into simple slogans. Some marketers have even resorted to using condescension to try to convince people to use screening programs (Figure 1).
Figure 1 – An old print ad from the American Cancer Society implied that women are crazy if they have not had a mammogram. Image taken from KERA News.[1]
These messages are not designed to help people make informed decisions; they are about getting people to behave or act a certain way. (If this sounds familiar to anything related to vaccination programs, you are not imagining it.)
Take prostate cancer. Every November, since 2003, men are encouraged to grow moustaches to raise awareness and promote screening: “grow a mo to save a bro” (others include Figure 2). Millions participate. Yet behind the cheerful campaign lies a yawning gap between what people believe prostate-cancer screening accomplishes and what the evidence shows.
Figure 2 – Online poster from Movember.com.
The research backing prostate screening is far from ubiquitously positive. Some estimates state that screening via prostate-specific antigen (PSA) tests, reduces prostate-cancer mortality by 8-44%.[2][3][4]Another indicates that mortality increases by 13% with screening.[5]Screening effectiveness varies substantially, depending on geographic region – European trials show greater benefit than those in the U.S. – likely reflecting differences in healthcare systems and screening practices.
When you balance screening against detecting indolent cancers, performing unnecessary biopsies, and exposing men to treatment-related complications, the overall benefit is modest.
One very recent example comes from a 23-year European follow-up study published a month ago in the New England Journal of Medicine.[6] [6] The study’s data were compatible with a 5–20% reduction in prostate-cancer mortality among men in a PSA screening program, compared to those who were not (Figure 3). However, in absolute terms, this means that a single invitation for screening reduced prostate cancer deaths by a small amount, roughly 1 in 456 men tested.
The remaining 455 men (99.8% of them) experienced no mortality benefit.
Figure 3 – Differences in the cumulative incidence of prostate-cancer-specific mortality in European men who were screened for prostate cancer (blue line) vs. not screened (grey line) over a 23-year follow-up period.
These results come with a catch: screened men were more likely to be diagnosed with prostate cancer, yet they did not live longer overall. Mortality from all other causes – an equally important metric – was identical between screened and unscreened groups (Figure 4).
Figure 4 – No difference in the cumulative incidence of mortality from all other causes in European men who were screened for prostate cancer (blue line) vs. not screened (grey line) over a 23-year follow-up period.
Put simply, screening increased the number of men labelled as cancer patients without extending their lives.
Why, then, are people still so enthusiastic about screening? Some might say it is because intuition often overrides data – despite typical statements to the contrary.
Others might say it is good marketing; the mantra “catch cancer early, and you can cure it” is powerful, simple, and reassuring. But real-world evidence is complicated. Some cancers grow so slowly that they never threaten a person’s health. Some grow so aggressively that even early detection and treatment cannot meaningfully change the outcome. And some sit in the middle – where screening might help, but it comes with tradeoffs.
The point is not that people should never be screened for cancer. Many people reasonably value the small chance of benefit over the risk of over-diagnosis, anxiety, and unnecessary treatment.
Even financial gain is dismissed in favour of testing. A U.S. telephone survey found that nearly 75% of respondents would rather receive a full-body CAT scan for cancer than receive $1,000 USD.[7]
To be fair, many physicians probably understand the tradeoffs involved in over-diagnosis and over-treatment. But people deserve to make decisions based on informed consent, not on slogans or endorsement.
For those who are healthy and are open to questioning the wisdom of screening, a book written by Gilbert Welch, Lisa Schwartz, and Steven Woloshin[8]may provide guidance the next time you are faced with the decision of whether to take a test or not, including:
- Why are you suggesting the test? This is a way to see if there is any external influence on your physician – including financial interests, or fear of legal retaliation from professional regulators.
- Are there any randomized controlled trials of the test?
- What does the test measure? Are you about to be hit by – to use an automotive example – a “check engine light”, or is it a signal of something more serious?
- What will we do if the test is positive? As a patient, if you do not want the follow-up procedure that results from a positive test, then maybe there is no reason to do the test.
Even after having these questions answered, a person may still want to be screened – and that is fine if it makes sense for you.
Ultimately, an individual’s decision comes down to a set of value judgements through which they can weigh being helped – catching cancer early – against the potential of worrying needlessly, and most importantly, being treated needlessly.
References
[1] KERA News. How America’s Largest Breast Imaging Company Markets Mammograms. Originally published: April 30, 2014
[2] Schröder FH, et al. Prostate-Cancer Mortality at 11-years Follow-up. NEJM 2012; 366(11): 981-90
[3] Hugosson J, et al. Mortality Results from the Göteborg Randomised Population-Based Prostate-Cancer Screening Trial. Lancet Oncol 2010;11(8): 725-32
[4] Martin RM., et al. Prostate-Specific Antigen Screening and 15-year Prostate Cancer Mortality: A Secondary Analysis of the CAP Randomized Trial. JAMA 2024; 331(17): 1460-70
[5] Andriole GL, et al. Mortality Results from a Randomized Prostate-Cancer Screening Trial. N Engl J Med 2009; 360(13): 1310-9
[6] Roobol MJ, et al. European Study of Prostate Cancer Screening— 23-Year Follow-up. NEJM 2025; 393: 1669-80
[7] CBC Radio. Ideas: You are Pre-Diseased – Part 2. Originally aired: April 20, 2010. Relevant discussion starts at: 38 minutes, 30 seconds
[8] Welch HG, Schwartz LM, Woloshin S. Over-Diagnosed: Making People Sick in the Pursuit of Health. Beacon Press; 2011
(Dr. David Vickers, BIG Media Ltd., 2025)
