Temporal Trends in Papillary and Follicular Thyroid Cancer Incidence from 1995 to 2019 in Adults in Denmark According to Education and Income

Background: Thyroid cancer incidence has increased over the past decades. Differences in incidence trends have been observed depending on socioeconomic status. Here, we describe trends in the incidence of papillary thyroid cancer (PTC) and follicular thyroid cancer (FTC) in Denmark by level of education and income. Methods: All PTC and FTC cases registered in the Danish Cancer Registry from 1995 to 2019 were identified. Individual-level information on education and income was obtained from nationwide registries. We calculated age-standardized incidence rates according to sex, tumor size, education and income, and estimated incidence trends by average annual percentage change (AAPC) and corresponding confidence intervals [CIs] for the periods 1995 to 2004 and 2005 to 2019 by using Poisson regression models. Results: We identified 3454 cases of PTC and 972 cases of FTC. From 2005 to 2019 among women, the incidence of PTC increased across all levels of education (AAPCshort education = 12.5% [CI 9.8 to 15.3]; AAPCmedium education = 8.1% [CI 6.4 to 9.9]; AAPClong education = 7.3% [CI 5.4 to 9.2]). The same pattern was seen for income. The incidence of FTC increased in all levels of education (AAPCshort education = 10.5% [CI 5.8 to 15.4]; AAPCmedium education = 4.0% [CI 0.9 to 7.3]; AAPClong education = 4.3% [CI 0.6 to 8.1]), with the same pattern for income. Similar trends were observed among men, in both small (≤2 cm) and large (>2 cm) PTCs and from 1995 to 2004 in both sexes. Conclusions: Enhanced detection of thyroid cancer among all levels of education and income cannot be ruled out, and in addition, our results may suggest a true increase in the incidence of differentiated thyroid cancer.