No overall increased risk of cancer in patients with rheumatoid arthritis: a nationwide dynamic cohort study in Taiwan

The association between rheumatoid arthritis (RA) and cancer is still controversial. This study aimed to estimate cancer incidence (both overall and site-specific) among patients with RA and to determine whether their cancer risk was higher than in the general population. We used the nationwide dynamic cohort from the National Health Insurance Research Database of Taiwan and obtained a total of 30,504 patients with no history of cancer who were newly diagnosed with RA between 1996 and 2008; they were followed up until 2010. Standardized incidence ratios (SIR) by age for various types of cancer were calculated in 5-year calendar periods by 5-year age intervals (quinquinquennium) to compare elevated risk of increasing age and increased cancer rate in later calendar years in Taiwan. During 225,432 person-years of follow-up, 1,595 cancers occurred, corresponding to 7.08 per 1,000 person-years. The SIR for all cancers was 0.93 (95 % CI 0.88-0.97). Most cancers were found in the first 2 years after diagnosis of RA, but the incidence decreased afterward. A significant excess of Hodgkin's lymphoma (SIR 3.31, 95 % CI 1.24-8.81) and non-Hodgkin's lymphoma (SIR 3.18, 95 % CI 2.64-3.83) was seen among patients with RA, whereas the risk of colorectal cancer was 29 % lower than the general population. In conclusion, this study showed that patients with RA do not have increased overall risk of cancers but have higher risk of hematologic malignancies and lower risk of colorectal cancer, than the general population.