Children with juvenile arthritis are four times more likely to develop cancer as other kids, a new study shows.
But the research, published in the medical journal Arthritis & Rheumatism, suggests that the powerful drugs used to treat the debilitating illness are not to blame. Rather it is the disease itself, which can wreak havoc with the immune system, that seems to hike cancer risk.
"This paper is good news. It provides reassurance that these drugs – which really improve the quality of life of these kids – are safe," Ronald Laxer, a staff rheumatologist at the Hospital for Sick Children in Toronto, said in an interview. He was not involved in the research.
Children with juvenile idiopathic arthritis are often treated with tumour necrosis factor inhibitors. In 2009, after more than a decade on the market, the U.S. Food and Drug Administration placed "black box" warning on the drugs, stating that they were associated with a higher risk of cancer.
This caused widespread consternation because, Dr. Laxer said: "These biologics have been dramatically helpful."
He said the increased risk of cancer in children with JIA is concerning but must also be kept in perspective.
Childhood cancer is rare – about 14 cases per 100,000 – so a four-fold increase still means juvenile arthritis sufferers have a low risk, about 64 per 100,000.
Children with juvenile arthritis experience symptoms similar to adults with rheumatoid arthritis including joint pain, swelling, tenderness and stiffness. The inflammation can be so damaging that they require joint replacements.
JIA affects about 10,000 Canadian children, according to the Canadian Arthritis Network.
The new study was conducted by a team led by Timothy Beukelman of the University of Alabama at Birmingham.
They used U.S. Medicaid records from 2000 to 2005 to identify 7,812 children with JIA, and compared their health outcomes with those of children with two other chronic conditions, asthma and attention-deficit hyperactivity disorder.
The rate of cancer was 4.4 times higher among the children with juvenile arthritis.
However, the research showed that cancer rates were more or less the same in JIA patients treated with TNF inhibitors, another commonly used drug called methotrexate and those who received little treatment.
"While children with JIA have a higher incidence of cancer compared to peers without JIA, the greater frequency of malignancy does not appear to be necessarily associated with treatment," Dr. Beukelman said.
About 19 per cent of juvenile arthritis sufferers were treated with TNF inhibitors, principally one drug etanercept. Another 44 per cent were treated with methotrexate, and 5 per cent with other immune modulating drugs. One-third of the children received no prescription drug treatments, though most take over-the-counter painkillers.
In a commentary also published in Arthritis & Rheumatism, Kenan Onel, a pediatric cancer researcher at the University of Chicago said the findings of the study "are at once concerning and reassuring for physicians, parents and patients."
He said that while there has been much concern about the cancer risk posed by drug treatments, "we have perhaps markedly understated the more significant risk of the disease itself."
Juvenile idiopathic arthritis is one of the most common chronic illnesses in children. In about half of cases, children go into remission, meaning their symptoms disappear. But the disease can do a lot of damage, which can limit the activities of JIA sufferers in childhood and through to adulthood.
Dr. Laxer said one of the most significant problems is that it tends to take a long time for children to be diagnosed, with their complaints often dismissed as growing pains.
"It's important for people to know that kids can get arthritis too, not just little old ladies," he said.