Comprehending thyroid cancer in Sri Lanka: current trends and outstanding questions

Background and Objectives: In Sri Lanka, thyroid cancer (TC) is the second commonest cancer among females and third commonest cancer in both sexes. The aim of the study was to describe the trend of TC according to sex, age and histology type in Sri Lanka from 2005-2019. Methods: Study analysed secondary data from the National Cancer Registry Sri Lanka. Age standardized rates (ASR) of thyroid cancer were extracted for the respective years. Age group specific incidence rates were calculated for each year under consideration. Join Point software version 4.9.0.0 was used to analyse trends. Best fit models reported, by Annual Percentage Change and Average Annual Percentage Change, 95% CI. A p-value <0.05 were taken as the level of significance. Results: Total 23363 TC cases analysed from 2005-2019. The ASR among women has increased threefold from 2005-2019 with an AAPC of 7.5% (95% CI 4.1- 11.1, p<0.05) and among males a two-fold rise was seen in ASR with AAPC being 8.0% (95% CI 5.5 - 10.6, P<0.05). Age-specific incidence rates were highest in ≥ 65year old males and 25-34 year old females. However, highest AAPC was seen in 35-44 age cohort in both sexes. Papillary TC was the main type of differentiated TC in both sexes. AAPC for overall papillary TC in females was 10.54% (95% CI 4.7-16.8, p<0.05) and 11.6% (95% CI 4.6-18.9, p<0.05) in males. Follicular TC showed a similar pattern with AAPC for females being 13.2% (95% CI 3.2-24.4 p<0.05) and 16.0% for males (95% CI 5.9-27.1, p<0.05). Conclusions: Incidence of TC in Sri Lanka reveals an increasing trend in both sexes. However, it is uncertain whether it is a true increase or due to better diagnosis and reporting. Therefore, further studies are recommended to explore the reasons for this observed increase.