Ethnic Background as a Determinant of Thyroid Cancer Risk: A Decade-Long National Cohort Study Reveals Divergent Epidemics in Saudi Arabia.

OBJECTIVES

To analyze and compare temporal trends, demographic characteristics, and stage at diagnosis for thyroid cancer (TC) between Saudi and non-Saudi populations in order to identify potential population-specific etiological drivers.

METHODS

We conducted a national retrospective cohort study of TC cases in Saudi Arabia from 2013-2022. To assess population-level trends, we computed age-standardized incidence rates (ASIRs) and multivariable Poisson regression alongside piecewise regression models for comparative analysis.

RESULTS

Among 14,159 total cases, TC incidence increased disproportionately in Saudi nationals, rising from 884 to 1,677 (90%), significantly outpacing the 184 to 275 (49%) increase observed in non-Saudis. The incidence rate ratio for Saudis versus non-Saudis was 5.67 (95% CI [5.41, 5.94]). Saudis presented with a significantly younger median age at diagnosis (5-10 years earlier, p < 0.001) and demonstrated a steeper annual increase in ASIRs (Interaction β = 0.0307, p < 0.001). A marked stage migration was concurrently observed among Saudi nationals, with localized diagnoses increasing from 55% to 71%. The recent period of the study (post-pandemic) revealed an acceleration in the Saudi cohort (+316.50 cases annually), a pattern absent in non-Saudis.

CONCLUSION

The profound divergence in incidence trends provides compelling evidence consistent with distinct, population-specific etiological drivers. This suggests a need to investigate genetic and environmental factors unique to the Saudi population. However, the heterogeneity of the non-Saudi comparator group necessitates cautious interpretation of the observed incidence rates.