Franklin J et al. (2006) Incidence of lymphoma in a large primary care derived cohort of cases of inflammatory polyarthritis. Ann Rheum Dis 65: 617–622

Lymphoma is more than twice as likely to occur in patients with inflammatory polyarthritis than in the general population, a UK study has shown—supporting previous findings of a causal link between the incidence of inflammatory polyarthritis (which includes rheumatoid arthritis [RA]) and lymphoma. Whether lymphoma develops as a consequence of immunosuppressive treatment, or of the characteristics of RA or inflammatory polyarthritis, however, remains unclear. So, Franklin et al. measured lymphoma risk in an unselected cohort of patients with inflammatory polyarthritis, and evaluated the effects of disease severity and treatment history on this risk.

This prospective, primary-care-based study recruited 2,105 patients enrolled on the Norfolk Arthritis Register (NOAR) between 1990 and 1999, who were recently diagnosed with inflammatory polyarthritis, and had accessible hospital records. During annual follow-up, data on prescription drug use and disease severity were collected.

After a total follow-up of 15,548 person-years, the incidence of lymphoma was 7.07 cases per 10,000 person-years. Lymphoma risk was highest in patients who had ever tested positive for rheumatoid factor, those ever diagnosed with RA, or those who had ever received disease-modifying antirheumatic drugs. Methotrexate use carried the highest risk (∼5 times that of the general population), although all these factors were interrelated.

The small number of lymphoma cases, however, meant that the authors could not draw definitive conclusions about the effects of disease severity and drug exposure on lymphoma risk. They highlight the need for appropriate control groups in future studies that explore the effects of antirheumatic drugs on lymphoma risk.