Children with juvenile arthritis develop cancer four times more often than children without the disease, but the treatments they receive --including biologic treatments like Enbrel - may not explain their increased risk, according to a new study.
If confirmed, researchers say the findings should ease fears that biologic treatments known as TNF inhibitors cause cancer in children and young adults.
But the study also raises new concerns about cancer risk linked to the rheumatic diseases for which the drugs are prescribed.
Cancer Concerns for Biologics Not New
Soon after the first TNF inhibitors became available almost 15 years ago, anecdotal reports of cancers in users of the drugs began surfacing.
Reports of malignancies in nearly 50 children prompted the FDA to require TNF-inhibitor manufacturers to include a "black box" warning on their labeling, alerting users about a possible cancer risk.
Last November, the agency announced that it would also require those manufacturers to perform "enhanced safety surveillance" on the drugs when used in children and adults under 30.
The newly reported study is among the largest ever to examine cancers in children with juvenile idiopathic arthritis (JIA), a disease that afflicts close to 300,000 children and teens in the U.S.
By analyzing Medicaid records from 2000 to 2005, researchers from the University of Alabama, Birmingham (UAB), identified 7,812 children with JIA. Their analysis also included comparison to more than 650,000 kids with asthma and close to 322,000 with attention deficit hyperactivity disorder (ADHD).
Compared to children without JIA, children with the rheumatic disease had a 4.4-times greater cancer risk. Treatment with a TNF inhibitor did not appear to influence this risk. The main TNF inhibitor reported used by children in the JIA group was Enbrel.
The study appears online in the journal Arthritis & Rheumatism.
Disease, Not Drugs, Raises Cancer Risk?
Cautioning that the results are preliminary, researcher and UAB associate professor of pediatrics Timothy Beukelman, MD, says the findings do not support the conclusion that TNF inhibitors are strongly linked to cancer.
He says a similar study from Sweden, which found a two- to three-fold greater cancer risk in JIA patients, came to a similar conclusion.
"It is unlikely that the increase was caused by these medications alone," he says. "At least part of this risk appears to be due to the disease itself."
Although the UAB study does not fully exonerate Enbrel and the other TNF inhibitors, pediatric cancer specialist Kenan Onel, MD, PhD, of the University of Chicago, calls the findings reassuring. Other TNF inhibitors include Humira, Kineret, Orencia, Remicade, and Rituxan.
"These drugs are very effective for the treatment of arthritis, so it is very reassuring to know that if they do carry a cancer risk it is probably very small," Onel says. "The not-so-reassuring news here is that just by having juvenile arthritis, a child may have an increased risk for cancer."
The study was funded by grants from the federal government's Agency for Healthcare Research and Quality (AHRQ), the U.S. Department of Health and Human Services, the FDA, and the National Institutes of Health.