Incidence of malignancy in primary Sjögren's syndrome in a Chinese cohort

Objectives. To evaluate the incidence of malignancies in a cohort of Chinese patients with primary Sjögren's syndrome (pSS) and to identify the risk factors of malignancy in pSS patients. Methods. A retrospective analysis was carried out in 1320 pSS patients who were recruited in Peking Union Medical College Hospital from 1990 to 2005 and were followed up for an average of 4.4 years. Among them, 29 patients developed malignancies. Standardized incidence ratios (SIRs) were calculated along with 95% CIs. Clinical characteristics were compared between patients with and without malignancies, as well as patients with haematological and non-haematological tumours. Results. Of the pSS patients, 2.2% developed malignancies during follow-up. Total SIR and SIR for lymphoma were 3.25 and 48.1, respectively. Different types of malignancy were observed including eight lymphomas, two myeloid myelomas and 19 solid tumours, which consisted of invasive thymoma, breast cancer, lung cancer, gastrointestinal adenocarcinoma, hepatoma, squamous cell carcinoma of tongue, uterine cervix cancer, renal carcinoma, thyroid carcinoma and mucoepidermoid carcinoma of parotid gland. Risk factor analysis showed that lymphadenopathy, enlargement of parotid glands, monoclonal immunoglobulin and absence of hypergammaglobulinaemia were correlated with malignancies. Conclusions. The current study confirms the increased incidence of lymphoma in Chinese patients with pSS, with the majority of B-cell non-Hodgkin's lymphoma. Associations between pSS and other malignant tumours such as myeloid myeloma, mouth cancer, breast cancer and thymoma need to be further observed.