The risk of cancer in patients with rheumatoid arthritis: a nationwide cohort study in Taiwan.

OBJECTIVE

The association of rheumatoid arthritis (RA) and malignancy has rarely been explored in Asian populations. The aim of this study was to investigate the relative risk of cancer in Taiwanese patients with RA and to identify groups of patients with a high risk of cancer.

METHODS

We conducted a nationwide cohort study of the risk of cancer among 23,644 patients with RA who had no history of malignancies, using the National Health Insurance database of Taiwan from 1996 to 2007. Standardized incidence ratios (SIRs) for various cancers were analyzed.

RESULTS

Among the patients with RA, 935 cancers were observed. Patients with RA had an increased risk of cancer (SIR 1.23, 95% confidence interval [95% CI] 1.22-1.23), especially hematologic cancers (SIR 2.74, 95% CI 2.68-2.81). The relative risk of cancer was higher among younger patients. Most cancer cases were detected within the first year following the diagnosis of RA. The relative risk of cancer decreased as the duration of observation increased. Among hematologic cancers, the risk of non-Hodgkin's lymphoma was greatest (SIR 3.54, 95% CI 3.45-3.63). Among solid tumors, the risk of cancers of the kidney and vagina/vulva was highest. A decreased risk of cancers of the cervix and nonmelanoma skin cancer in patients with RA was also observed.

CONCLUSION

Patients with RA have an increased risk of cancer, especially hematologic and kidney cancers. The relative risk of cancer in patients with RA decreased with long-term followup. Cancer screening with continued vigilance is recommended for patients with RA.