Cancer in rheumatoid arthritis: occurrence, mortality, and associated factors in a South European population

OBJECTIVES: To estimate the prevalence, incidence, mortality, and predictors of cancer in patients with rheumatoid arthritis (RA). METHODS: We compared the incidence of cancer and the mortality by cancer in a cohort of 789 randomly selected RA patients (1999-2005) with the expected ones in the general population. We estimated standardized incidence ratios (SIR) and standardized mortality ratios (SMR) by indirect age and sex standardization. Additionally, we analyzed by generalized linear models the association of various predictors with cancer incidence, obtaining incidence rate ratios (IRR) with 95% confidence intervals (CI). RESULTS: The SIR of cancer in RA is 1.23 (95% CI: 0.78-1.85). By cancer type, there is an increased risk of leukemia, non-Hodgkin's lymphoma, and lung cancer in RA compared with the general population of the same sex and age. The SMR of cancer is 1.0 (95% CI: 0.53-1.7). By cancer type, RA patients with lung or kidney cancer have higher mortality than expected. Being male, elderly, with longstanding disease, and having used any cytotoxic drugs apart from methotrexate are confirmed as predictive factors for cancer. Additional independent predictors are increases in blood leukocyte counts (IRR per 3000 u/mm3 increase: 1.88 (95% CI: 1.6 -2.1)) and decreases in serum hemoglobin (IRR per 2 g/l decrease: 1.88 (95% CI: 1.19 -2.94)). CONCLUSIONS: The overall incidence and mortality of cancer in RA is not greater than the expected, although there is an increased risk of hematopoietic and lung cancers in RA patients compared with the general population. Hemoglobin and leukocyte counts may help to identify RA patients at risk for cancer.