Trends in Incidence and Survival of Patients With Thymic Epithelial Tumor in a High-Incidence Asian Country: Analysis of the Korean Central Cancer Registry 1999 to 2017

Introduction: To report the trends in incidence and survival associated with thymic epithelial tumors (TETs) in Korea. Methods: Data from 1999 to 2017 were obtained from the Korean Central Cancer Registry. Age-standardized incidence rates and average annual percentage changes (AAPCs) were calculated. Net survival (NS) was estimated by the Pohar-Perme method. Results: Among 5812 patients diagnosed with having TETs, 58.9%, 38.1%, and 3.0% were diagnosed with having thymoma, thymic carcinoma, and thymic neuroendocrine tumor (NET), respectively. Age-standardized incidence rates were 0.50, 0.30, 0.18, and 0.02 per 100,000 for all TETs and the respective subtypes. There was an increase in incidence of all TETs (AAPC = 6.1%) and subtypes: thymoma (AAPC = 5.6%), thymic carcinoma (AAPC = 7.0%), and thymic NET (AAPC = 3.4%). Proportions of patients with thymoma, thymic carcinoma, and thymic NET were 58.9%, 38.1%, and 3.0%, respectively. For thymoma, the relative proportion of distant stage decreased (19.4% in 2005 to 8.8% in 2017) and low-grade WHO subtype (A, AB, B1) increased faster than high-grade WHO type (B2, B3) (AAPC = 19.8% versus 9.6%). For thymoma, the 5-year NS was 82.3%. This increased from 64.3% in 1999 to 2002 to 90.6% in 2013 to 2017. For thymic carcinoma, the 5-year NS was 46.2% and only slightly increased from 39.4% in 1999 to 2002 to 47.9% in 2013 to 2017. Conclusions: This study indicates a high incidence of TET and its continuous increase in Korea. The proportion of thymic carcinoma was relatively higher than in the United States or Europe. Survival for thymoma improved during the study period, whereas this was not evident for thymic carcinoma or thymic NET.