Xeljanz may be linked to an increased risk of cancer, according to recent clinical trial results — adding to the list of potentially serious side effects of the autoimmune drug.

The U.S. Food and Drug Administration (FDA) recently warned of a potential link between Xeljanz and cancer, though a warning for this particular risk hasn’t been added to the drug’s labeling. This potential cancer risk joins other Xeljanz side effects such as heart issues and life-threatening blood clots.

Pfizer’s ORAL Surveillance study was ordered by the FDA to evaluate the medication’s safety profile after approval. The clinical trial included 4,362 patients who were treated with one or two doses of Xeljanz or a tumor necrosis factor (TNF) inhibitor medication. All study participants were over the age of 50 and had at least one cardiovascular risk factor.

Unfortunately, the study revealed that Xeljanz patients may face an increased risk for cancer. The most common cancer seen in Xeljanz patients was lung cancer. However, breast cancer, melanoma, prostate cancer, and pancreatic cancer were also recorded in the Xeljanz group.

The study also showed that Xeljanz patients may be at risk for heart-related problems. The most common heart issue recorded was heart attacks.

“Providing information on the safe and effective use of our medicines is imperative,” said Pfizer Chief Medical Officer of Inflammation and Immunology Tamas Koncz in the company’s press release.

“We believe that extensive additional analyses of these study data, and communicating them as soon as possible, will further clarify the benefit and risk profile of tofacitinib to help inform medical decision making and patient care.”

Both Pfizer and the FDA note that final trial data is not available and that these conclusions are based on preliminary data only. Further warnings or notices may be released when final data is available.

Xeljanz (tofacitinib) was approved by the FDA in 2012 as a treatment for rheumatoid arthritis. In 2017, a second use was approved – the treatment of psoriatic arthritis. The third authorization came in 2018 when the FDA approved Xeljanx for ulcerative colitis treatment. The medication treats these three autoimmune conditions by suppressing the immune system.

In 2019, preliminary results from the ORAL trial showed that Xeljanz patients may be at risk for a clotting condition known as deep vein thrombosis. With DVT, blood clots form in the deep veins of the legs and can travel through the body to the lungs. Blood clots in the lungs, also known as pulmonary embolism (PE), can be life threatening.

The FDA added the most prominent boxed warning to Xeljanz packaging to warn patients and doctors of the risk of blood clots and death with the higher 10 mg twice daily dose.