The risk of non-Hodgkin’s lymphoma (NHL) in people with primary Sjögren’s syndrome, an autoimmune disease that affects the moisture-producing glands in the body, is nine times higher compared to the general population, according to a Norwegian study published in Arthritis Care & Research.

Past studies have shown a link between primary Sjögren’s syndrome and NHL, a cancer that develops in the lymphatic system (part of the immune system), which includes the lymph nodes and the spleen. But because of differences in study design and disease definition, the exact risk was not known.

The Norwegian researchers say they found the risk of lymphoma for Sjögren’s patients to be lower than expected. “Study results show that the actual risk is lower than previously described, but our findings are supported by other recent studies,” says study co-author Svein Joar A. Johnsen, MD, who specializes in internal medicine at Stavanger University Hospital in Norway.

Dr. Johnsen and his colleagues looked at nearly 897,000 inhabitants living in two counties on the west coast of Norway. With the use of a population-based Sjögren’s registry, they identified 443 patients with a diagnosis of primary Sjögren’s syndrome. (Primary Sjögren’s occurs by itself, while secondary Sjögren's occurs in people with another autoimmune disease like rheumatoid arthritis or lupus.)

Of these patients – who were followed for an average of almost nine years – seven lymphoma cases developed. When they compared it to the risk of NHL in a person from the general population, they found the risk to be nine times greater.

“People shouldn’t panic over this. The probability is still really low,” says Eric L. Matteson, MD, chair of rheumatology at the Mayo Clinic in Rochester, Minn.

But he does caution that because people with Sjögren's are at increased risk, they should pay attention to any symptoms relating to non-Hodgkin’s lymphoma, including weight loss, swollen lymph nodes and fevers.

The reason why the diseases are connected may have something to do with inflammatory cells affecting the immune system. “There may be genetic information in these cells that causes them to become cancerous,” Dr. Matteson says.

People with RA are also at higher risk of developing lymphoma. But the risk isn’t as high as it is for those with primary Sjögren's, according to Dr. Matteson. “Lymphoma risk is two to four times greater for people with RA than those without RA,” he says.