We conducted a retrospective cohort study to examine cancer risk in a large cohort of systemic lupus erythematosus (SLE) patients in California. The cohort consisted of individuals with SLE derived from statewide patient discharge data during the period 1991-2002. SLE patients were followed using cancer registry data to examine patterns of cancer development. Standardized incidence ratios (SIRs) and 95% CI were calculated to compare the observed to expected numbers of cancers based on age-, race-, and sex-specific incidence rates in the California population. The 30,478 SLE patients were observed for 157,969 person-years. A total of 1,273 cancers occurred within the observation interval. Overall cancer risk was significantly elevated (SIR = 1.14, 95% CI = 1.07-1.20). SLE patients had higher risks of vagina/vulva (SIR = 3.27, 95% CI = 2.41-4.31) and liver cancers (SIR = 2.70, 95% CI = 1.54-4.24). Elevated risks of lung, kidney, and thyroid cancers and several hematopoietic malignancies were also observed. Individuals had significantly lower risks of several screenable cancers, including breast, cervix, and prostate. These data suggest that risks of several cancer types are elevated among SLE patients. Detailed studies of endogenous and exogenous factors that drive these associations are needed.
