Age-standardized incidence, mortality rate, and trend changes of thyroid cancer in the Balearic Islands during the 2000-2020 period: a population-based study.

Objective: Global thyroid cancer (TC) incidence is growing worldwide, but great heterogenicity exists among published studies, and thus, population-specific epidemiological studies are needed to adequate health resources and evaluate the impact of overdiagnosis.

Methods: We conducted a Public Health System database retrospective review of TC incident cases from 2000 to 2020 in the Balearic Islands region and evaluated age-standardized incidence rate (ASIR), age at diagnosis, gender distribution, tumor size and histological subtype, mortality rate (MR), and cause of death. Estimated annual percent changes (EAPCs) were also evaluated and data from the 2000-2009 period were compared to the 2010-2020 period when neck ultrasound (US) was routinely performed by clinicians at Endocrinology Departments.

Results: A total of 1387 incident cases of TC were detected. Overall, ASIR (×105) was 5.01 with a 7.82% increment in EAPC. A significant increase in the 2010-2020 period was seen for ASIR (6.99 vs 2.82, P < 0.001) and age at diagnosis (52.11 vs 47.32, P < 0.001) compared to the 2000-2009 period. A reduction in tumor size (2.00 vs 2.78 cm, P < 0.001) and a 6.31% increase in micropapillary TC (P < 0.05) were also seen. Disease-specific MR remained stable at 0.21 (×105). The mean age at diagnosis for all mortality groups was older than survivors (P < 0.001).

Conclusion: The incidence of TC has grown in the 2000-2020 period in the Balearic Islands, but MR has not changed. Beyond other factors, a significant contribution of overdiagnosis to this increased incidence is likely due to changes in the routine management of thyroid nodular disease and increased availability of neck US.