Abstract
OBJECTIVE: To assess racial and sex variances in second primary thyroid malignancy (SPTM) cumulative incidence and temporal trends and the radiation exposure effect in pediatric SPTM. MATERIALS AND METHODS: A retrospective cohort study, a non-experimental epidemiologic design, was used to assess the cumulative incidence (CmI) and temporal trends as well as the exposure effect of radiation in SPTM among children, 0-19 years, in the Surveillance, Epidemiology, and End Results (SEER) registry, National Cancer Institute (NCI), USA. Percent change (PC) and annual percent change (APC) were used to examine CmI rates and temporal trends, while chi-square statistics and binomial regression models were used to examine variable distribution by race and to determine the exposure effect of radiation on SPTM as well as mortality, respectively. RESULTS: The frequency of pediatric thyroid cancer was (n = 3457) between 1973 and 2013/14, while the PC was 151.2 for all races but 99.8 among whites. Of all pediatric thyroid cancers diagnosed during this period, SPTM accounted for 3% (n = 99). Compared to whites, blacks/AA were 60% less likely to present with SPTM, adjusted risk ratio, aRR = 0.40, 99% CI 0.06-2.47, while other races were 18% more likely to develop SPTM, aRR = 1.18, 99% CI 0.48-2.87. Additionally, females relative to males were 63% less likely to be diagnosed with SPTM, aRR = 0.37, 99% CI 0.22-0.61. With respect to urbanicity, compared to children in rural areas, those in urban areas were 21% less likely to develop SPTM, aRR = 0.79, 99% CI, 0.12-5.35, while children in metropolitan areas were 40% less likely to develop SPTM, aRR = 0.60, 99% CI, 0.10-3.59. Although imprecise, there was a 5% increased risk of SPTM, with radiation as an exposure effect, aRR = 1.05, 99% CI 1.01-1.75. CONCLUSIONS: There are increasing temporal trends in pediatric SPTM with blacks relative to whites having observed lower incidence, despite an increasing percent change among blacks/AA, indicative of the disproportionate burden of this malignant neoplasm. SPTM risk was higher among males and in rural areas, while radiation as a risk for SPTM was clinically and biologically meaningful, albeit an observed statistically insignificant inference due to sampling variability, requiring intervention mapping in radiation exposure margination among children.