Representing Thyroid Cancer Epidemiology in the US Over Time: A Microsimulation Modeling Approach Incorporating Temporal Differences in Thyroid Ultrasound Utilization by Sex and Age

OBJECTIVES: Although thyroid cancer mortality remained stable between 1992 and 2018 (0.4-0.5 per 100,000), incidence increased dramatically (5.7 to 13.1/100,000), which has been attributed primarily to the detection of subclinical papillary thyroid carcinomas (PTC). More than 40% of all thyroid cancers diagnosed are subclinical PTCs (less than 2 cm). Detection and treatment of PTCs have a major impact on the costs and the quality of life of patients, and exposes them to unnecessary treatment risks. We developed the PApillary Thyroid CArcinoma Microsimulation model (PATCAM) to replicate thyroid cancer epidemiology in the U.S. over time. No similar microsimulation thyroid cancer model has been developed before.

METHODS: PATCAM simulates thyroid cancer-related events experienced by all individuals in the US from age 15 until death in birth cohorts starting from 1920 using highly detailed natural history and detection components. PATCAM was built using high-quality real-world data including age and sex-specific thyroid ultrasound referral and biopsy rates and a novel calibration method. PATCAM was externally validated against three active surveillance studies including the largest and longest running thyroid cancer active surveillance cohort in the world (from Japan) and two from the US.

RESULTS: PATCAM successfully replicated sex-, age- and stage-specific PTC incidence and mortality from SEER database between 1975 and 2018. External validation experiments demonstrated that PATCAM’s predictions on the proportion of fast-growing tumors aligned well with the reported rates from active surveillance studies. PATCAM successfully modeled the significant increase in the incidence until 2010s, followed by a leveling off since then by incorporating temporal differences in thyroid ultrasound usage across sex and age groups.

CONCLUSIONS: PATCAM provides an externally validated analysis platform to identify factors that influence the detection of subclinical PTCs and to assess the effects of interventions that cannot feasibly be evaluated by prospective trials.