Background Patients with rheumatoid arthritis (RA) have an increased risk to develop lymphomas. In a previous case-control study we found a strong association between high disease activity in RA and the risk of lymphoma.

To get a better understanding of the biological background of this connexion we examined lymphoma subtypes in RA patients.

Objectives To study the distribution of lymphoma subtypes in RA patients compared to the general population.

Methods In a population-based cohort of 11,683 patients with RA in the Uppsala Health Care region in Sweden,42 cases of lymphoma were identified through record linkages with the Swedish cancer registry 1965 through 1984.

The medical records and paraffin embedded lymphoma tissues were collected.

The lymphomas were reclassified according to the recently described REAL classification. The distribution was compared to lymphoma subtypes in the general population according to the Non-Hodgkin´s Lymphoma (NHL) Classification Project.¹

Results One patient was excluded as the RA diagnosis was wrong. Tissues from 36 of the remaining patients were found and reviewed. NHL was found in 33 patients, Hodgkin´s disease in 2 and 1 patient did not have lymphoma.

Compared with the expected there was a more than 2-fold increased number of diffuse large B-cell lymphoma (22 patients,69% of NHL´s compared with 31% expected).

Few of the patients had been treated with immunosuppressive drugs.

Conclusion The distribution of lymphoma subtypes in RA patients differs from the expected.

This supports the idea of a specific underlying mechanism behind lymphoma development in RA patients. This mechanism may also be of importance for RA development and activity. Genetics and other characteristics of those RA patients who develop lymphomas deserve further studies.

Reference

1. The Non-Hodgkin’s Lymphoma Classification Project: A Clinical Evaluation of the International Lymphoma Study Group. Blood 1997;89(11):3909–18