Objective: Rurality is associated with higher incidence and higher disease-specific mortality for most cancers. Outcomes for rural and ultrarural ("frontier") patients with thyroid cancer are poorly understood. This study aimed to identify actionable deficits in thyroid cancer outcomes for rural patients. Methods: We queried linked California Cancer Registry and California Office of Statewide Health Planning and Development databases for patients diagnosed with thyroid cancer (1999-2017). We analyzed time from disease stage at diagnosis, time from diagnosis to surgery, receipt of appropriate radioactive iodine ablation, surveillance status, and overall and disease-specific mortality for urban, rural, and frontier patients. Cox and logistic regression models controlled for clinical and demographic covariates a stepwise manner. All incidence figures are expressed as a proportion of newly diagnosed cases. Results: Our cohort comprised 92,794 subjects: (65,475 women [70.6%]; mean age 50.0 years). Compared to urban patients, rural and frontier patients were more likely to be American Indian, White, uninsured, and from lower quintiles of socioeconomic status (p < 0.01). Distant disease at diagnosis was more common in rural (56.0 vs. 50.4 cases per 1000 new cases, p < 0.01) and frontier patients (80.9 vs. 50.4 per 1000, p < 0.01) compared to urban patients. The incidence of medullary thyroid cancer was greater in rural patients (17.9 vs. 13.6 cases per 1000, p < 0.01) and frontier patients (31.0 vs. 13.6 per 1000, p < 0.01) compared to urban patients. The incidence of anaplastic thyroid cancer was higher in frontier versus urban patients (15.5 vs. 7.1 per 1000, p < 0.01). When compared to urban patients, rural and frontier patients were more often lost to follow-up (odds ratio [OR] 1.69 [confidence interval, CI 1.54-1.85], and OR 3.03 [CI 1.89-5.26], respectively) and had higher disease-specific mortality (OR 1.18 [CI 1.07-1.30], and OR 1.92 [CI 1.22-2.77], respectively). Rural and frontier residence was independently associated with being lost to follow-up, suggesting that it is a key driver of disparities. Conclusion: Compared to their urban counterparts, rural and frontier patients with thyroid cancer present with later-stage disease and experience higher disease-specific mortality. They also are more often lost to follow-up, which presents an opportunity for targeted outreach to reduce the observed disparities in outcomes.
Keywords: disparities; rural; thyroid cancer; urban.