Temporal Associations Between Thyroid Cancer Epidemiological Trends and Classification Revisions

Background/Objectives: This study evaluated potential temporal associations between international histopathological classifications, staging updates, and the long-term divergence observed between papillary thyroid cancer (PTC) and follicular thyroid cancer (FTC) incidence trends. Applying an advanced statistical protocol comprising the recursive Supremum Chow Test, Piecewise Segmented Regression with Regime Switching (PSR-RS), and a non-linear Markov-Switching Intercept and Slope (MSIA) model, we analyzed population-level annual incidence rates (AIR) in the United States from 1975 to 2023.

Methods

We implemented a two-pronged approach to identify and validate structural trend changes in incidence trends. Approach 1 tracked endogenous, data-driven incidence shifts, while Approach 2 tested the fixed calendar milestones corresponding to the official publication dates of major classifications. Crucially, this multistage analytical protocol was applied directly to the individual PTC and FTC series, as well as to the scale-independent log ratio, ln(PTC/FTC) and aggregate diagnostic gap timelines.