Incidence of malignancy in Japanese patients with rheumatoid arthritis

Abstract

To determine the incidence of malignancy and site-specific malignancies in Japanese patients with rheumatoid arthritis (RA). In a prospective large observational cohort study named IORRA, 7,566 patients with RA were enrolled from April 2001 to April 2005 and were followed up to October 2005. Occurrence of malignancy was originally collected by patient reports of IORRA survey biannually from April 2001 to October 2005, and was confirmed by medical records. Standardized incidence rate (SIR) of the observed-to-expected cancer incidence and 95% confidence intervals (95% CI) were then calculated. Factors obtained at first enrollment in IORRA were assessed for association with risk of malignancy using the Cox proportional hazards model. A total of 177 malignancies in 173 patients (58 in men, 115 in women) were identified during the observation period of 25,567 person-years. The age- and sex-standardized incidence rate of malignancy was 437.1 (men, 706.8; women, 366.1) per 100,000 person-years. The SIR of malignancy was slightly excess (SIR 1.18, [95% CI 1.02-1.37]) in all patients, but 1.29 (95% CI 0.99-1.67) in men, and 1.13 (95% CI 0.94-1.36) in women. A significant excess of lymphoma (SIR 6.07, [95% CI 3.71-9.37]) and lung cancer (SIR 2.29, [95% CI 1.57-3.21]), whereas decreased incidence of colorectal cancer (SIR 0.49, [95% CI 0.26-0.83]), were found. Male gender and older age were identified as risk factors for malignancy. A slight excess in the incidence of overall malignancy and highly excess of lymphoma in Japanese RA patients was demonstrated.