When South Korean doctors launched a nationwide thyroid cancer screening programme, diagnoses shot up 15 fold. Yet the death rate from thyroid cancer didn't budge. More patients were being created than lives were being saved.
Authors
- Ahmed Elbediwy
Senior Lecturer in Cancer Biology & Clinical Biochemistry, Kingston University
- Nadine Wehida
Senior Lecturer in Genetics and Molecular Biology, Kingston University
It is a clear illustration of a problem that is quietly reshaping how doctors think about cancer: overdiagnosis . Not misdiagnosis but the accurate detection of tumours that would not actually harm the patient.
Modern cancer screening is rightly celebrated as one of medicine's great achievements. Finding cancer early saves lives. But as technology has become ever more sensitive, are we sometimes doing more harm than good?
Better detection
A cancer doesn't spring from a single rogue cell flicking a switch. It develops through multiple steps , and many clusters of abnormal cells never complete that journey.
Some sit quietly in the body for decades. Only a fraction ever become life threatening. The problem is that once an abnormality is detected and labelled as cancer, it triggers a chain reaction - anxiety, aggressive treatment, serious side-effects - for a condition that might never have caused the patient any trouble at all.
Twenty years ago, many of these abnormalities would have been impossible to find. Today, state-of-the-art imaging and highly sensitive detection tests can identify tiny clusters of abnormal cells , faint genetic changes, and the smallest growths. As that technology improves, the boundary between a dangerous cancer and a harmless biological quirk becomes increasingly blurred.
This raises an uncomfortable question about rising cancer rates, particularly the well documented increase in diagnoses among the under-50s . Is this a genuine biological shift - cancers becoming more aggressive and appearing earlier in life - or is it partly a reflection of the fact that today's younger adults are being screened, scanned and monitored far more intensively than previous generations?
Thyroid cancer is the starkest example. In South Korea in 2011 , that 15-fold surge in diagnoses came almost entirely from screening, not from any real increase in disease. Researchers and clinical bodies eventually revised their guidelines in 2013, moving away from screening slow-growing lesions and towards monitoring rather than immediate surgery.
Prostate cancer tells a similar story. The introduction of the prostate-specific antigen (PSA) test produced a large jump in diagnoses, but death rates stayed flat - suggesting many men were being treated for cancers that grow so slowly, they never would have become life-threatening.
The consequences were serious. Surgery left many men incontinent or impotent, with no improvement in survival. Guidelines now favour active surveillance for many prostate growths.
For these two types of cancers, also those of the colon , the evidence increasingly points in the same direction: "watchful waiting" is often safer than immediate intervention. Surgery, radiotherapy and chemotherapy all carry significant risks and long-term side effects . Exposing a patient to those risks for a tumour that was never going to threaten their life is difficult to justify.
None of this means early detection should be abandoned. For fast-moving cancers - pancreatic, lung, some breast cancers - finding the disease early remains critical. The challenge is learning to distinguish between the cancers that demand urgent action and those that can safely be watched. That requires not just better technology, but better judgement about when to use it.
Fairness and transparency
Shifting towards a risk-based approach to screening also raises difficult questions about fairness and transparency. Who gets screened, how often and on what grounds? Those decisions carry real consequences, and they deserve a more open public debate than they currently receive.
What is becoming clearer, though, is that the old logic of cancer screening - find it, remove it - is no longer sufficient on its own. Overdiagnosis is a genuine harm, even if it is a less visible one than a missed diagnosis. For some patients, learning to live carefully with a monitored cancer may turn out to be safer than trying to eliminate it entirely.
The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
