Association Between Eight Autoimmune Diseases and Thyroid Cancer: A Nationwide Cohort Study.

Background: It has often been reported that thyroid-specific autoimmune diseases (ADs), such as Hashimoto's thyroiditis and Graves' disease, could increase the risk of thyroid cancer, but the association between other ADs beyond thyroid and thyroid cancer has not been well investigated. This study aimed to examine the risk of thyroid cancer in patients with eight ADs compared with those without ADs. Methods: This nationwide retrospective matched cohort study was conducted to investigate the relationship of eight ADs (Hashimoto's thyroiditis, Graves' disease, type 1 diabetes mellitus, Sjogren's disease, inflammatory bowel disease [IBD], vitiligo, systemic lupus erythematosus, and rheumatoid arthritis [RA]) with the risk of incident thyroid cancer using the National Health Insurance Service-National Sample Cohort. The Cox-proportional hazard model was used to estimate the adjusted hazard ratio (HR) and confidence intervals (CI) for thyroid cancer in relation to each of AD compared with control group without AD. Results: During the average follow-up of 9.49 years, 138 thyroid cancer cases were newly developed in control group and 268 cases were occurred in group with 8 ADs. For all of study participants, the risk of thyroid cancer was significantly increased in patients with Hashimoto's thyroiditis (HR = 2.10 [1.57-2.81]), Graves' disease (HR = 2.67 [1.99-3.62]), IBD (HR = 2.06 [1.50-2.83]), vitiligo (HR = 1.71 [1.13-2.59]), RA (HR = 1.76 [1.07-2.90]), and total of 8 ADs (HR = 1.97 [1.60-2.42]) compared with control group without ADs. When ADs were divided into three types, thyroid-specific ADs (HR = 2.37 [1.85-3.03]) showed the strongest and significant association with thyroid cancer, followed by local ADs (HR = 1.83 [1.41-2.38]), and systemic ADs (HR = 1.77 [1.14-2.74]). Conclusions: Specific ADs-especially for thyroid-specific AD, vitiligo, IBD, and RA-were associated with increased risk for thyroid cancer.