Malignancies during follow-up in an epidemiologically defined systemic lupus erythematosus inception cohort in southern Sweden

The objective of this study was to identify all malignancies in an inception cohort of SLE patients in southern Sweden and compare with the observed frequencies and spectrum of malignancies in the general population. All adult incidence cases of SLE in a defined population during the period 1981-1996 were retrieved from a prospective database and the cases were followed to endpoint or through 1998. The SLE cohort registry was aggregated with the National Cancer Registry to identify all malignancies by date, type and outcome. Standardized morbidity rates (SMR) were calculated based on the sex- and age-matched general population of the region. Sixteen malignancies occurred in 13 patients out of a total of 116 SLE patients observed for 1086 patient-years. The SMR for all cancers detected was 2.24 (confidence interval 0.6-5.7) for males and 1.02 (confidence interval 0.4-2.1) for females and thus indicative of no general increase in malignancies. However, the SMR for non-Hodgkin lymphoma was 11.63 (confidence interval 1.4-42.0), for pulmonary cancer 5.55 (confidence interval 0.7-20.1) and prostatic cancer 6.41 (confidence interval 1.3-18.7) all significantly increased. The increase in prostatic carcinoma disappeared when only cases occurring after a latency period of 3y after SLE diagnosis were included. In this comprehensive inception cohort of SLE no increase in relative risk of malignancy overall was found, but the frequencies of non-Hodgkin lymphoma and pulmonary cancer were increased, possibly also the frequency of prostatic carcinoma.