Thyroid cancer in adolescents and young adults: a population-based study in 185 countries worldwide

Cancer burden among adolescents and young adults (AYAs) aged 15-39 years has increased during the past two decades, with thyroid cancer being a major contributor. We aimed to comprehensively evaluate trends and the current burden of thyroid cancer among AYAs globally.

We obtained annual incidence and mortality data of thyroid cancer from the Cancer Incidence in Five Continents Plus and the WHO Mortality databases. Temporal trends were displayed using the average annual percent changes of age-standardised incidence rates estimated during 2003-2017. The national estimates of incidence and mortality of thyroid cancer and other cancer types for 185 countries in 2022 were obtained from the GLOBOCAN platform. Incidence-to-mortality ratios were compared by cancer type. We estimated the correlation of human development index (HDI) with thyroid cancer incidence and mortality.

Thyroid cancer incidence rates among AYAs have increased rapidly since the 2000s in most countries, whereas mortality rates remained stably low. Notable increases in incidence were found in South Korea, Cyprus, Ecuador, and Türkiye, with particularly pronounced rises in China. During 2003-2017, the average annual percent changes of thyroid cancer incidence were greater than 10% in six countries and greater than 5% in 19 countries. In 2022, there were approximately 237 000 new cases and around 2100 deaths from thyroid cancer, ranking among the top three most diagnosed cancers in 100 countries for females and in 26 countries for males. By 2022, thyroid cancer accounted for 20·3% of all new cancer cases in female AYAs and 13·6% in male AYAs, ranking as the second most diagnosed cancer among female AYAs, after breast cancer, and the most common cancer among male AYAs. Thyroid cancer incidence rates varied greatly by country, continent, and HDI, while mortality rates were less variable. The incidence-to-mortality ratios for thyroid cancer among AYAs exceeded 3300 for females and 600 for males (<100 for other cancer types) in some countries. HDI was strongly and positively correlated with thyroid cancer incidence, whereas its association with mortality was negative but weak.

The epidemiological profile of thyroid cancer among AYAs indicates a large expansion of overdiagnosis to younger populations. Increased efforts are required to prevent unnecessary diagnosis and treatment due to overuse of diagnostic procedures.

Guangzhou Science and Technology Project, Guangdong Basic and Applied Basic Research Foundation, Italian Association for Cancer Research, Italian Ministry of Health, and Young Talents Program of Sun Yat-sen University Cancer Center.