Rheumatoid arthritis(RA) is a disorder with altered immunologic function and increased risk of developing malignancies, while studies examining the association between hepatocellular carcinoma (HCC) and RA remain lacking. The investigators aimed to investigate the risk of HCC between participants with and without RA.

The investigators did a retrospective, observational, nested case-control study in a cohort that was previously recruited from a population-based RA survey. All participants were enrolled prospectively in Taiwan's national health insurance between Jan 1, 1999, and June 30, 2009, and had follow-up data until Dec 31, 2009. RA was diagnosed based on the 1987 American College of Rheumatology diagnostic criteria. The investigators matched RA and non-RA subjects by propensity score in a 1:1 ratio. The primary outcome was the risk of developing HCC. Cox proportional hazards regression was applied to estimate the hazard ratio (HR) and 95% confidence interval (CI) of HCC for RA and non-RA cohort.

Inclusion Criteria:

• subjects were required to have ≥2 RA diagnosis (International Classification of Diseases, Ninth Revision [ICD-9-CM]-codes 714.0x), and to be ≥18 years of age on the date of first diagnosis. And inclusion in the Registry for Catastrophic Illness Patient Database (RCIPD)

Exclusion Criteria:

• who were diagnosed with RA only once during the study interval, <18 years of age when first diagnosed with RA, first diagnosed with RA after July 1, 2009, or not registered in the RCIPD were excluded

All individuals were enrolled prospectively in Taiwan's national health insurance between Jan 1, 1999, and June 30, 2009, and had follow-up data until Dec 31, 2009

The Taiwan's National Health Insurance Research Database (NHIRD) between Jan 1, 1999, and June 30, 2009, and had follow-up data until Dec 31, 2009. The Taiwan's NHIRD contains health-care data gathered prospectively for 99% of Taiwan's population and approximately 22,600,000 individuals in 2007. The Taiwan's National Health Research Institutes (NHRI) maintained the NHIRD and provided it to the investigators for research purposes. De-identified data were further scrambled before being released to public access for research. The accuracy of diagnosis of major diseases in the NHIRD, such as stroke and acute coronary syndrome, has been validated previously.