Risk of non-Hodgkin's lymphoma and thyroid cancer in primary Sjögren's syndrome measured using the Korean Health Insurance Claims Database

Objective. The aim of this study was to evaluate the incidence and risk of non-Hodgkin's lymphoma (NHL) and thyroid cancer in patients with primary Sjögren's syndrome (pSS) using the Korean National Health Insurance Service (NHIS) claims database. Methods. pSS was identified using the Korean NHIS medical claims database between 2007 and 2017. The case definition required more than one visit based on the SS diagnostic code and the registration system for rare and incurable diseases. We included all admissions with a primary diagnosis of lymphoma and thyroid cancer. Results. The pSS incidence was 1.88 cases/100,000 inhabitants. Female patients had a higher incidence than male patients, with a female-to-male ratio of 7.65:1. Of those, we identified 18 (0.34%), 1 (0.02%) and 29 (0.56%) patients with NHL, Hodgkin's disease and thyroid cancer, respectively. For pSS, the standardised incidence ratios for NHL and thyroid cancer were 6.32 (95% confidence interval [CI] 4.09-9.38) and 1.23 (95% CI 0.88-1.68), respectively. Compared with the general population, female patients with pSS had a 6.95-fold higher risk of developing NHL, while the male patients did not. Patients with pSS did not have a higher risk of developing thyroid cancer. Conclusion. Although pSS is associated with a higher risk of developing NHL, the risk of NHL appears to have decreased compared with that in previous studies. Our study suggests that the risk of NHL or thyroid cancer with SS is not higher than that reported in previous studies.