The basis of racial differences in the incidence of thyroid cancer

Background: The incidence of thyroid cancer in black Americans is half that in white Americans. It is unknown whether this gap represents a population difference in disease or is attributable to inferior cancer screening in the black population. Methods: A population-based cohort study of 53,990 patients (1973-2003) was performed using the National Cancer Institute's Surveillance Epidemiology End Results database. Socioeconomic variables were explored using the Healthcare Cost and Utilization Project database and macroeconomic data. Results: Since 1973, thyroid cancer incidence among whites has increased 150.2% (4.0 to 9.9 of 100,000), while incidence among blacks has increased 73.2% (3.0 to 5.1 of 100,000). Across 17 regions, the incidence correlated with the percentage of the population with health insurance (r = 0.56, P = .02). Regression analysis suggested that half of the black-white incidence gap might be attributable to differences in health insurance status. Patients with thyroid cancer were more likely to be insured or reside in wealthier ZIP codes. Black patients were more likely to present at advanced age (RR 1.08, P < .0001) and with tumors >4 cm in size (RR 1.13, P <.0001). Black patients were slightly less likely to present with advanced disease (RR 0.96, P = .0008). Cancer-specific mortality was identical in the two populations. Discussion: Sociodemographic data and differences at presentation support a small detection disparity in thyroid cancer, which may contribute to part of the incidence gap. However, this effect is not sufficiently strong to fully explain the incidence gap. A population difference in the incidence of disease may be coexistent.