If you have rheumatoid arthritis, you may be concerned about reports that suggest you are at higher risk for also developing lymphoma. Before you worry unnecessarily, here's what you need to know about the link between these two diseases.

What is Lymphoma?

Lymphoma is a form of cancer that affects white blood cells, or lymphocytes. Lymphocytes are part of the immune system and help fight disease and infection.

There are two major forms of lymphoma: Hodgkin's lymphoma and non-Hodgkin lymphoma. Lymphomas may be fast or slow growing, and physicians further categorized lymphomas by the type of cell in which they originate. Non-Hodgkin lymphoma is far more prevalent; the National Cancer Institute estimates 65000 new cases in 2009 versus 8,500 new cases of Hodgkin's Lymphoma.

Is There a Link?

Early studies showed an association between non-Hodgkin's lymphoma in rheumatoid arthritis patients who were taking asathioprine, an immune-suppressing drug. Other studies showed a similar link in a small number of patients who were taking methotrexate.

Later studies found mixed evidence of a link between lymphoma and rheumatoid arthritis patients who took TNF-inhibiting drugs (also called biologics). TNF is a protein that promotes inflammation and is associated with painful, swollen joints and bone tissue destruction in rheumatoid arthritis. Ironically, physicians originally used TNF-inhibiting drugs to eliminate tumors in cancer patients.

The most recent studies still show a link between lymphoma and rheumatoid arthritis. However, researchers say the level of disease activity in arthritis patients explains the association, rather than the use of biologics. They've found that the risk of developing lymphoma is greatest in rheumatoid arthritis patients with the highest cumulative disease activity.

In a large study of 75,000 rheumatoid arthritis patients, patients who had medium disease activity had an eight-fold increase in the likelihood of developing lymphoma, while patients with high disease activity had a 70-fold increase in risk. In a reversal of cause and effect, researchers believe suppressing rheumatoid arthritis with aggressive treatment may actually decrease the odds of developing lymphoma. For example, patients who use corticosteroids long term to manage their rheumatoid arthritis symptoms appear to be less likely to develop lymphoma.

The Bottom Line

Despite these disturbing statistics, it's important to realize that although there seems to be a clear, elevated risk of lymphoma in patients with rheumatoid arthritis, the risk is still very low: less than five percent.