Risk of Prostate Cancer in US Veterans With Rheumatoid Arthritis

Objective Patients with rheumatoid arthritis (RA) have an increased risk of select cancers, including lymphoma and lung cancer. Whether RA influences prostate cancer risk is uncertain. We aimed to determine the risk of prostate cancer in patients with RA compared to patients without RA in the Veterans Health Administration (VA). Methods We performed a matched (up to 1:5) cohort study of male patients with and without RA in the VA from 2000 to 2018. RA status, as well as covariates, were obtained from national VA databases. Prostate cancer was identified through linked VA cancer databases and the National Death Index. Multivariable Cox models compared prostate cancer risk between patients with RA and patients without RA, including models that accounted for retention in the VA system. Results We included 56,514 veterans with RA and 227,284 veterans without RA. During 2,337,104 patient‐years of follow‐up, 6,550 prostate cancers occurred. Prostate cancer incidence (per 1,000 patient‐years) was 3.50 (95% confidence interval [95% CI] 3.32–3.69) in patients with RA and 2.66 (95% CI 2.58–2.73) in patients without RA. After accounting for confounders and censoring for attrition of VA health care, RA was modestly associated with a higher prostate cancer risk (adjusted HR [HRadj] 1.12 [95% CI 1.04–1.20]). There was no association between RA and prostate cancer mortality (HRadj 0.92 [95% CI 0.73–1.16]). Conclusion RA was associated with a modestly increased risk of prostate cancer, but not prostate cancer mortality, after accounting for relevant confounders and several potential sources of bias. However, even minimal unmeasured confounding could explain these findings.