Global landscape of early-onset thyroid cancer: current burden, temporal trend and future projections on the basis of GLOBOCAN 2022.

Background: With rapid social-economic development and widespread screening, the surge in incidence and overdiagnosis of thyroid cancer is more worrying among the young than the general population. This problem, however, still lacks adequate attention.

Methods: We retrieved the original data of current, past and future burden of thyroid cancer from the Global Cancer Observatory (GLOBOCAN) 2022. We calculated the age-specific mortality-to-incidence ratio (MIR) by dividing age-specific mortality rates by incidence rates to quantify potential overdiagnosis, and used Segi's world standard population to calculate the age-standardised incidence rate (ASIR) and age-standardised mortality rate (ASMR). We then assessed the correlation between the human development index (HDI) and ASIR/ASMR using the linear correlation coefficient (r). Lastly, we characterised the temporal trend with the estimated annual percentage change (EAPC) and project the early-onset thyroid cancer burdens to 2050.

Results: Globally, there were an estimated 239 362 (ASIR = 4.00 per 100 000 population) cases and 2409 (ASMR = 0.04 per 100 000 population) deaths from thyroid cancer among individuals aged <40 years in 2022. Compared to its ranking as the 7th most common cancer in the overall population, thyroid cancer rose to become the 2nd most common cancer among individuals <40 years. Nearly 99% of thyroid cancer cases in individuals <40 years of age (MIR = 0.01) may be potentially overdiagnosed, whereas 34% of cases in those >80 years (MIR = 0.66) were overdiagnosed. The ASIR of early-onset thyroid cancer varied widely (from 0.13 to 13.17 per 100 000 population), while the ASMR remains relatively similar and low across different regions. The ASIR of early-onset thyroid cancer increased with HDI (r = 0.69), while the ASMR decreased (r = -0.22). The ASIR of early-onset thyroid cancer had the fastest upward trend (EAPC in males vs. females: 9.88 vs. 9.28%) compared to early-onset cancers at other sites, while ASMR showed a downward trend (EAPC in males vs. females: -0.38% vs. -1.33%). The Republic of Korea experienced the highest EAPC for early-onset thyroid cancer ASIR (males vs. females: 29.95% vs. 23.04%). If national rates from 2022 remain stable, projected cases of early-onset thyroid cancer would decrease in high (-13.3%) and very high (-10.9%) HDI countries, but increase in low (96.5%) and medium HDI countries (11.7%).

Conclusions: The trend of early-onset thyroid cancer at the global level is more alarming than that of thyroid cancer overall. The younger age at diagnosis of thyroid cancer, the higher risk of potential overdiagnosis. Without timely interventions, the thyroid cancer burden will inevitably become a serious global public health issue, especially for the young population.