To evaluate hypotheses about the relationship between immune alterations and cancer, several investigators have determined cancer incidence in groups of patients with rheumatoid arthritis (RA), a chronic autoimmune disease. The primary finding has been an increased risk of hematopoietic cancers.
In this study, we have attempted to refine estimates of the association between RA and subsequent development of specific cancers.
We investigated site-specific cancer risk associated with RA in a population-based cohort study of 11683 Swedish men and women with a hospital (inpatient) diagnosis of RA. These case patients were identified from 1965 to 1983 and had follow-up through 1984 by computer linkage of the Swedish Hospital Inpatient Register to the National Swedish Cancer Registry (840 case patients with cancer) and the Swedish Registry of Causes of Death. Cancer risk was estimated by standardized incidence ratios (SIRs) for specific cancers.
For men and women overall, there were decreased risks for cancers of the colon (SIR = 0.63; 95% confidence interval [CI] = 0.5-0.9), rectum (SIR = 0.72; 95% CI = 0.5-1.1), and stomach (SIR = 0.63; 95% CI = 0.5-0.9) and an increased risk for lymphomas (SIR = 1.98; 95% CI = 1.5-2.6).
The reduced risk for colorectal cancer in patients with RA is consistent with previous studies of RA patients and with reports which state that use of nonsteroidal anti-inflammatory drugs may protect against the development of large bowel cancers. The excess of lymphomas also confirms a number of earlier investigations of RA patients.