Methotrexate (MTX) is a disease-modifying anti-rheumatic drug (DMARD) commonly prescribed to RA patients. A link between the drug and cancer has been suggested, and there are even concerns that the drug itself may be carcinogenic, but research examining this concern has proven inconclusive.

This new study included 459 RA patients (309 women, 150 men) who started treatment with MTX prior to June 1986. During a total of 4,273 person-years of follow up (an average of 9.3 years per patient), 87 cancers were identified.

The researchers found that the RA patients who received MTX were 50 percent more likely than people in the general population to develop cancer of any kind. In terms of specific cancers, the RA patients had more than a fivefold increased risk of non-Hodgkin lymphoma, a threefold increased risk of melanoma, and almost a threefold increased risk of lung cancer.

The increased risk levels for non-Hodgkin lymphoma and lung cancer were similar to the findings of studies in Europe and in the United States. However, the increased risk for melanoma identified in this study was new.

"This study is, to our knowledge, the first to report an increased risk of melanoma in patients with RA treated with MTX compared with the general population," lead author Dr. Rachelle Buchbinder said in a prepared statement.

"Futher investigation is needed to determine whether this risk is unique to Australia and what role MTX, immunosuppression per se, and/or environmental factors such as exposure to UV radiation play in its development," she said. "Our findings, taken together with other studies investigating the risk of skin cancer in patients with RA, may support a role for regular skin cancer screening for all patients with RA, particularly those receiving immunosuppressive therapy."

The study was published in the June issue of the journal Arthritis Care & Research.