Some patients who take immunotherapy drugs to treat their cancer may develop inflammatory arthritis, says a study from Johns Hopkins Medicine. Researchers found that the drugs ipilimumab and nivolumab increase the risk for autoimmune and joint diseases, such as arthritis.

"I don't think anyone is particularly surprised that rheumatologic disorders might be a complication of drugs that boost the immune system," says study author Laura C. Cappelli, M.D., a rheumatologist at the Johns Hopkins University School of Medicine.

While the study found that a small number of patients — 1.3 percent — developed autoimmune diseases, Cappelli says the rate is actually higher since patients with only mild joint disease or those whose health was already deteriorating, may not have been referred to the rheumatology clinic for their symptoms.

"In 2015, our rheumatology clinic started getting more and more referrals from our oncology department to evaluate patients treated with immunotherapies," says Cappelli. "And the patients we saw had very severe, highly inflammatory arthritis. They needed even higher doses of steroids to control their symptoms compared to what is needed in other forms of inflammatory arthritis, like rheumatoid arthritis."

Ipilimumab and nivolumab — as well as a growing number of other checkpoint inhibitors now in clinical trials — are designed to turn off the molecular "checkpoints" that some cancers use to evade the body's natural immune system cells.

When the drugs work, they allow the immune system to detect — and attack — tumor cells. But because they also turn up the activity of the immune system as a whole, the drugs can trigger immune-related side effects, including so-called autoimmune responses, in which the body attacks its own cells and tissues.

Cappelli says that clinical trials of ipilimumab and nivolumab found an increased risk of inflammatory bowel diseases, lung inflammation, autoimmune thyroid disease and pituitary gland inflammation. But those trials were designed primarily to determine efficacy against cancer and not to fully examine all features of rheumatologic side effects, she notes.

Cappelli says she wants the case report to raise awareness among both patients and clinicians that rheumatologic side effects may occur with the drugs. "It is important when weighing the risk-benefit ratio of prescribing these drugs," says. "And it’s important for people to be on the lookout for symptoms so they can see a rheumatologist early in an effort to prevent or limit joint damage."

The article was published in the Annals of the Rheumatic Diseases.