By Scott Baltic

The findings come from pooling data from several studies, in a so-called meta-analysis.

"Previous studies appeared contradictory, with studies finding either higher, lower or equal rates of cancer in patients with rheumatoid arthritis compared with the general population," Dr. Samy Suissa of McGill University Health Centre, Montreal, told Reuters Health. "Our meta-analysis brings some clarity; the studies were not contradictory at all. Indeed, it was not overall cancer that should have been looked at, but the site-specific cancers."

The highest risk observed for a specific malignancy in people with rheumatoid arthritis was for lymphoma, the team reports in Arthritis Research & Therapy, with a 2-fold greater risk than in the general population. The risk of lung cancer among rheumatoid arthritis patients was 63 percent higher than in the general population.

Conversely, the risks of colorectal and breast cancer were lower in people with rheumatoid arthritis than in the general population, at 23 percent and 16 percent, respectively.

The researchers found the overall risk of malignancy for people with rheumatoid arthritis was "near parity" with the general population.

"Clinicians treating patients with rheumatoid arthritis should be on the lookout for possible early signs of lung cancer and lymphoma," Suissa advised.