Risk of cancer among rheumatoid arthritis patients in California

The objective of this retrospective cohort study was to evaluate cancer risk among rheumatoid arthritis (RA) patients in California. The study cohort derived from statewide patient discharge records was followed via linkage with cancer registry data over the period 1991-2002. Age and sex adjusted standardized incidence ratios (SIRs) and 95% confidence intervals were calculated to compare observed to expected numbers of cancers based on age, race, and sex specific incidence rates in the California population. Among the 84,475 RA patients, who were observed for 405,540 person-years, 5,533 incident cancers were diagnosed during the observation interval. The risk of developing lymphohematopoietic cancer was significantly higher in the cohort for both sexes. Males had significantly higher risks of lung, liver, and esophageal cancer, but a lower risk of prostate cancer. Females were at significantly decreased risk for several cancers including breast, ovary, uterus, cervix, and melanoma, with the risk reduction ranging from 15 to 57% lower than the general population. Hispanics had increased risks of leukemia, vagina/vulva, lung, and liver cancers. Studies investigating the mechanisms that underlie the reported associations between RA and specific cancer types are needed.