Association of Screening by Thyroid Ultrasonography with Mortality in Thyroid Cancer: A Case-Control Study Using Data from Two National Surveys.

Background: The incidence of thyroid cancer is increasing worldwide due to an increased detection of small well-differentiated papillary thyroid carcinomas. This study aimed to evaluate the effect of screening with ultrasonography on deaths from thyroid cancer. Materials and
Methods: We conducted a matched case-control study using data from two sources representative of the adult Korean population. Cases were selected from the National Epidemiologic Survey of Thyroid Cancer database, and controls were selected from the Korean National Cancer Screening Survey database. Controls were individually matched to case patients with respect to age, sex, and area with a ratio of 10:1. The primary outcome was death from thyroid cancer. Controls were required to have been alive on the date of thyroid cancer diagnosis in the corresponding case.
Results: The analysis included 120 patients who died from thyroid cancer and 1184 controls. Compared with those who had never been screened, the odds ratios for death from thyroid cancer among those who had been screened were 1.44 (95% confidence interval [CI] 0.68-3.05) if cases with missing information on screening were excluded and 1.13 [CI 0.49-2.63] if all cases were included, and missing information was imputed. Stratification by sex, year of diagnosis, and histological type did not show any statistically significant relationships between screening with ultrasonography and death from thyroid cancer, regardless of the statistical model used. Conclusions: Screening for thyroid cancer with ultrasonography does not prevent death from thyroid cancer; therefore, screening asymptomatic adults for thyroid cancer is unwarranted.