Increase in incidental detection of thyroid cancer in Osaka, Japan.

Using Osaka Cancer Registry data, we examined age-specific and age-adjusted incidence rates of thyroid cancer according to the route of thyroid cancer detection from 1992 to 2012. The detection routes were categorized into "symptomatic" and "incidental detection." Age-specific incidence rates of incidentally-detected thyroid cancer consistently increased during the study period, especially after 2001, for all sex and age groups other than childhood. The rate of symptomatic thyroid cancer did not largely differ among groups. Age-adjusted incidence rates of symptomatic thyroid cancer were around 1.5 and 4.5 per 100 000 among men and women, respectively. The rate of incidentally-detected thyroid cancer increased from 0.1 and 0.1 per 100 000 person-years among men and women in 1992-1994 to 2.0 and 4.9, respectively, in 2010-2012. Age-adjusted mortality rates among both sexes during the study period leveled off. This finding suggests that the thyroid cancer incidence rate in Osaka increased with incidental detection. We need to continue careful monitoring to confirm these findings.