IARC 60th Anniversary - 19-21 May 2026
Session : 19/05/26 - Posters
Overdiagnosis of thyroid cancer in adolescents and young adults in 63 countries worldwide: a population-based study.
ASANGBEH-KERMAN S. 1, WANG Y. 1,2, DAL MASO L. 3, RUMGAY H. 1, PIZZATO M. 1,4, VACCARELLA S. 1, LI M. 5
1 IARC, Lyon, France; 2 Department of Epidemiology and biostatistics, School of Public Health, Peking University / Key laboratory of Epidemiology of Major Diseases, Ministry of Education, Beijing, China; 3 Cancer Epidemiology Unit, Centro di Riferimento Oncologico di Aviano IRCCS, Aviano, Italy; 4 Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy; 5 Department of Cancer Prevention, State Key Laboratory of Oncology in South China, Guangdong Provincial Clinical Research Center for Cancer, Sun Yat-sen University Cancer Center, Guangzhou, China
Background
Thyroid cancer represents one of the most striking examples of cancer overdiagnosis worldwide. A recent study estimated that more than 1.7 million individuals may have been overdiagnosed with thyroid cancer in 63 countries across a 5-year period, corresponding to about 74% of all diagnosed cases. This phenomenon disproportionately affects adolescents and young adults (AYAs, 15-39 years old), particularly young women. In this age group, thyroid cancer incidence has increased rapidly since the 2000s in most regions of the world, while mortality has remained relatively stable and at low levels, or has declined.
Objective
We aim to estimate thyroid cancer overdiagnosis among AYAs during 2013-2017 across 63 countries worldwide.
Methods
The annual incidence of thyroid cancer by sex and five-year age groups for AYAs 15-39 years old was obtained from the International Agency for Research on Cancer (IARC) Cancer Incidence in Five Continents (CI5) Plus, for the most recent period (2003–2017) for 97 registries across 43 countries.
Sex-age-specific thyroid cancer cases, along with corresponding population counts, were retrieved from CI5 Volume XII, which includes data from 460 population-based cancer registries in 65 countries for the period 2013-2017. Countries with fewer than ten incident cases were excluded, and national data were used in preference to regional data when both were available, resulting in the inclusion of 385 registries across 63 countries to quantify overdiagnosis. We estimated expected age-specific thyroid cancer incidence rates under a counterfactual scenario without overdiagnosis by assuming that historical age-specific incidence patterns (well described by a power-law function prior to the widespread use of ultrasonography and intensified thyroid surveillance) would have been maintained. Excess incidence, defined as the difference between observed and expected age-specific rates and incidence cases, was interpreted as overdiagnosis. All analyses were conducted in R (version 4.5.1).
Results
Thyroid cancer incidence rates among AYAs increased in almost all countries during 2003-2017. The average annual percent changes of thyroid cancer incidence rates were above 10% in six countries (China, Chile, Latvia, Ecuador, Cyprus, and Poland) and generally above 5% in 19 countries for both sexes. The fastest increases were found in China, with an average annual percent change of 20·8% in females and 27·6% in males from 2003 to 2017. Estimates of thyroid cancer overdiagnosis among adolescents and young adults (AYAs) will be presented at the conference, with analyses currently ongoing and final estimates expected by May 2026.
Conclusion
Intensified thyroid surveillance and the widespread use of increasingly sensitive diagnostic technologies capable of detecting indolent tumours have led to substantial overdiagnosis of thyroid cancer among AYAs, despite clinical guidelines consistently recommending against screening in asymptomatic individuals. Understanding the extent of thyroid cancer overdiagnosis in this population is essential to reducing avoidable harms in young people and to improve health system inefficiency.