Population-based data from Cyprus show why rising thyroid-cancer incidence should neither be automatically dismissed as overdiagnosis nor used to justify indiscriminate detection.
By Prof. Loizos Loizou
Thyroid cancer is being diagnosed increasingly among adolescents and young adults, particularly females. The central question is no longer whether incidence is rising, but why.
A major international study led by the International Agency for Research on Cancer (IARC), covering adolescents and young adults aged 15–39 years in 185 countries, recently documented rapidly increasing incidence in many populations while mortality remained very low and relatively stable. The investigators concluded that overdiagnosis is probably a major driver of the global increase. Cyprus was among the countries showing particularly rapid rises (1).
The overdiagnosis argument is persuasive. Wider use of ultrasound and other imaging can detect small, subclinical thyroid cancers that might never have caused symptoms or threatened life. Finding such cancers can lead to surgery, lifelong thyroid-hormone replacement, psychological burden and other consequences without necessarily improving health.
But does overdiagnosis explain all of the increase?
Our population-based findings from Cyprus suggest that the answer may be more complex.
What did we find in Cyprus?
Using the Paediatric Oncology Registry of Cyprus (PORCY), we studied thyroid cancer diagnosed in children and adolescents aged 0–19 years between 1998 and 2017.
We identified 81 cases, 76.5% in females. The age-standardised incidence rate was approximately 16 per million per year, placing Cyprus among populations with some of the highest reported rates internationally. Papillary thyroid carcinoma accounted for 86.4% of cases. Incidence increased significantly over time; among adolescents aged 15–19 years, the annual percentage change was approximately 7.6% (2).
But the most interesting finding emerged when we looked beyond total case numbers and examined stage at diagnosis.
Comparing 2008–2017 with 1998–2007, localised thyroid cancer increased 1.71-fold, but this increase was not statistically significant. In contrast, regional metastatic disease increased 3.76-fold, a statistically significant increase. One distant metastatic case occurred in the second decade and none in the first (2).
This distinction matters.
Overdiagnosis may explain part of the rise-but perhaps not all of it
If increased detection of small, clinically insignificant thyroid cancers were the only mechanism operating, one might expect the increase to be concentrated predominantly in localised disease.
That was not what we observed.
The substantial increase in regional disease does not prove that there has been a genuine biological increase in thyroid carcinogenesis. Cyprus has a small population and therefore relatively small case numbers. Improvements in ultrasound and staging could also increase the detection of regional lymph-node involvement.
These limitations are important.
Nevertheless, the findings make it difficult to assume that overdiagnosis alone explains the entire pattern.
Our study therefore raises a question rather than claiming to provide a final answer: could improved detection and a genuine increase in disease occurrence be operating simultaneously?
The possible explanations require investigation. They include changes in diagnostic intensity and healthcare practices, but also genetic susceptibility, hormonal influences, ionising radiation, environmental exposures, dietary factors including iodine-related factors, and other determinants that remain poorly understood.
Importantly, previous cancer treatment did not explain the Cyprus findings: only one case in our series was a second primary thyroid cancer following earlier cancer therapy (2).
Avoiding two opposite errors
The debate should therefore not become a choice between aggressively looking for thyroid cancer and dismissing rising incidence as merely an artefact of modern medicine.
Both overdiagnosis and underdiagnosis matter.
Indiscriminate ultrasound examination of asymptomatic, low-risk young people risks discovering abnormalities that may never become clinically relevant. Conversely, clinically significant thyroid nodules, suspicious cervical lymph nodes and individuals with recognised risk factors should not be ignored because of concern about overdiagnosis.
The appropriate response is risk-based diagnosis and management: careful clinical assessment, expert ultrasound when indicated, biopsy of appropriately selected suspicious lesions, specific surveillance of high-risk individuals and multidisciplinary management that matches treatment intensity to disease risk. Current European paediatric thyroid guidelines similarly emphasise expert multidisciplinary care and risk-adapted investigation and treatment (3).
We need to know not only how many cancers we find-but what cancers we find
The Cyprus experience illustrates a broader epidemiological lesson.
Increasing incidence alone cannot tell us whether we are witnessing better detection, overdiagnosis, a genuine increase in disease occurrence-or some combination of these.
We need high-quality population-based registries, together with information on age, sex, tumour characteristics, stage at diagnosis and changes in diagnostic practice (4).
The objective should not be to find every possible microscopic thyroid cancer.
But neither should we automatically explain every increase as overdiagnosis.
The real challenge is to identify the cancers that matter, avoid unnecessary intervention, and continue investigating why clinically significant thyroid cancer may also be increasing.
References
1. Li M, Dal Maso L, Pizzato M, Rumgay H, Vaccarella S. Thyroid cancer in adolescents and young adults: a population-based study in 185 countries worldwide. Lancet Diabetes Endocrinol [Internet]. 2026 Feb 1 [cited 2026 Sep 29];14(2):112–22. Available here.
2. Loizou L, Demetriou A, Erdmann F, Borkhardt A, Brozou T, Sharp L, et al. Increasing incidence and survival of paediatric and adolescent thyroid cancer in Cyprus 1998–2017: A population-based study from the Cyprus Pediatric Oncology Registry. Cancer Epidemiol [Internet]. 2021;74(June):101979. Available here.
3. Lebbink CA, Links TP, Czarniecka A, Dias RP, Elisei R, Izatt L, et al. 2022 European Thyroid Association Guidelines for the management of pediatric thyroid nodules and differentiated thyroid carcinoma. Eur Thyroid J [Internet]. 2022;11(6). Available here.
4. Loizou L, Demetriou A, Erdmann F, Borkhardt A, Brozou T, Sharp L, et al. Patterns and temporal trends in the incidence of childhood and adolescence cancer in Cyprus 1998–2017: A population-based study from the Cyprus Paediatric Oncology Registry. Cancer Epidemiol [Internet]. 2022 Oct 1 [cited 2022 Oct 6];80:102239. Available here.
Author information
Prof. Loizos G. Loizou
Professor of Medicine, University of Nicosia, Cyprus
President, ELPIDA Foundation for Children with Cancer and Leukemia
Founder, Paediatric Oncology Registry of Cyprus (PORCY)
Head, Cyprus International Action Plan for Childhood and Adolescent Cancer (Cy-IAPCC).
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