Abstract

Background: Thyroid cancer is one of the most common malignancies of the endocrine system, the fifth most common malignancy in women worldwide, and the second most common cancer in women over 50 in 2019. It is the sixth most common cancer in both sexes and the third most common cancer in women in Guilan province. This study was conducted to describe the geographic variation and investigate any changes in the trend of the thyroid cancer incidence rate. Methods: This study was conducted on the data of the Guilan University of Medical Sciences cancer registration system. The crude and age-standardized incidence rate was calculated per 100,000 person-years. Joinpoint regression analysis evaluated the time trends and annual percent changes (APC). The incidence rate was estimated separately for each city and high-risk areas were shown on the province map using GIS software. Results: 1742 cases of thyroid cancer (83.7 in women and 16.3 in men) were registered in Guilan province from 2009 to 18. The incidence of thyroid cancer was 5.1-fold higher in women than men. The results of the joinpoint regression analysis showed that the age-standardized incidence rate of thyroid cancer in both sexes has increased significantly over ten years (APC: 26.4; 95 CI: 22.5–30.4), (P-value < 0.001). In our study, Astaneh-ye Ashrafiyeh, Lahijan, and Langarud cities were identified as high-risk areas of the province for both sexes. Conclusion: The trend of incidence of thyroid cancer in Guilan province is increasing. Also, a wide geographical variation was found in the incidence of thyroid cancer. © 2024 Elsevier Ltd