Sex-Specific Trends in Thyroid Cancer Incidence and Histological Patterns in Northern Tunisia: A Population-Based Study with Implications for Cancer Control and Prevention

Background: Thyroid cancer (TC) represents the most common endocrine malignancy worldwide, with incidence increasing rapidly across diverse geographic regions. However, population-based evidence from North Africa remains limited, and comprehensive longitudinal analyses examining sex-specific incidence patterns, histological subtypes, and trends in tumor extension are lacking in Tunisia. Aim: This study aimed to (i) quantify TC incidence trends by sex and age group, (ii) characterize histological subtype-specific temporal patterns and tumor extension at diagnosis in northern Tunisia between 2000 and 2018, and (iii) to address projections in incidence by sex until 2040. Methods: A retrospective, population-based registry study was conducted using data from the Northern Tunisia Cancer Registry (NTCR), covering 11 governorates with a population of 5,233,700 in 2018. All primary invasive TC cases diagnosed between 2000 and 2018 were included (n = 3639). Age-standardized incidence rates (ASIRs) were calculated using the WHO standard population. Temporal trends were assessed using Joinpoint regression to estimate average annual percentage change (AAPC) with 95% confidence intervals. Projections of TC incidence to 2040 were generated using Bayesian autoregressive age–period–cohort models. Results: TC incidence increased significantly between 2000 and 2018, with overall ASIR rising from 2.8 to 5.0 per 100,000 person-years (AAPC = 3.8%, p < 0.001). In males, ASIR increased from 0.9 to 2.4 (AAPC = 3.0%, p < 0.001), while in females it rose from 3.7 to 7.8 (AAPC = 4.3%, 95% CI: 3.0–5.7; p < 0.001). The increase was predominantly driven by papillary thyroid carcinoma (PTC) (AAPC = 6.4% in males; 5.8% in females; both p < 0.001), whereas follicular thyroid carcinoma (FTC) remained stable. Notably, the proportion of metastatic cases decreased significantly in females (AAPC = −7.2%, p = 0.033), and the proportion of regionally advanced disease decreased in males (AAPC = −5.0%, p = 0.034). Conclusions: This population-based study demonstrates a sustained rise in TC incidence in northern Tunisia, disproportionately affecting women and largely driven by papillary histology. The concurrent increase in TC incidence alongside a reduction in regional and metastatic extension at diagnosis occurred. These findings have important implications for cancer prevention and control, highlighting the need for risk-adapted screening strategies and rationalized diagnostic practices.