Incidence of cancer in a cohort of patients with primary Sjogren's syndrome

Objective. To compare the incidence of subsequent cancers in a cohort of patients with primary Sjogren's syndrome (pSS) with that of the general population in the same region of England. Methods. A retrospective analysis was carried out on 112 patients who had attended the out-patients department at University College Hospital, London, from 1979 onwards. Patients were followed up from diagnosis of pSS to diagnosis of first subsequent cancer, death, loss to follow-up or 31 December 2003 (the censoring date) to determine the person-years at risk for each individual. The expected numbers of subsequent cancers were calculated from sex-/age-/period-specific rates for the general population of southeast England, derived from registrations at the Thames Cancer Registry. Standardized incidence ratios (SIRs) were then calculated as the ratio of observed to expected numbers of cancers, along with 95% confidence intervals (CIs). Separate analyses were performed for all malignant cancers combined, lymphomas and non-lymphoid cancers. Results. Among the 112 patients with pSS, 25 developed cancer (either before or after development of pSS), with lymphoma occurring in 11 cases. Nine patients had two cancers. There was a significantly elevated incidence of lymphomas in pSS patients compared with the general population (SIR 37.5, 95% CI 20.7-67.6). For non-lymphoid cancer, the observed increase in incidence was small and not statistically significant (SIR 1.5, 95% CI 0.9-2.6). Conclusion. This study confirms that there is an increased incidence of lymphoma in patients with pSS. An increase in the incidence of other cancers was not proven but the observation that some patients developed more than one cancer raises the possibility that there may be a subgroup of patients who are at greater risk of developing cancer.