The risk of developing non-Hodgkin lymphoma and the mortality rate in primary Sjögren's syndrome: a single-centre, retrospective cohort study.

Primary Sjögren's syndrome (pSS) is a systemic autoimmune disease that is manifested by the sensation of dry eyes and dry mouth. The higher incidence of non-Hodgkin lymphoma (NHL) among pSS has already been extensively researched. However, there are uncertanties whether the mortality risk in pSS patients and in pSS patients with NHL is increased. The purpose of this study was to describe the prevalence of NHL among pSS patients and to calculate their mortality risk. We retrospectively analysed data on 1367 patients treated in our rheumatology department under the ICD-10 code M35.0. The study finally recruited 155 patients who met the 2016 ACR/EULAR criteria for the diagnosis of pSS. Descriptive statistics was used in data analysis. We applied the indirect standardization by age to compare the incidence rate of NHL in our cohort to general population. Additionally, we compared the mortality in our study to the general population by calculating the standardized mortality ratio (SMR). The overall incidence rate of NHL was 440 per 100,000 patient-years. The SIR compared to the general population was 30.13 (95% CI 12.87-54.63). The overall mortality rate of pSS patients in our cohort was nearly identical to that of the general population (SMR = 0.98 [95% CI (0.47-1.69)]). This study confirms that there are significant differences in lymphoma prevalence, histology, and prognosis across the studied populations. Furthermore, this study found that patients with pSS have similar mortality risk as the general population, and no patient in our cohort died from NHL.