In June 2006, the FDA allowed the drug back on the market but with strict conditions governing its use.
Just last month, the FDA approved Tysabri to treat people with a moderate to severe form of Crohn's disease.
But there is basic science to support Mullen's observations.
One of the participants in an earlier study of Tysabri had developed (and subsequently died of) a metastatic melanoma that appeared as soon as he got his first dose of the drug, Mullen said.
And in a study done before Tysabri received FDA approval, melanomas in mice that were given the drug had an increased tendency to detach from the primary tumor and spread.
Tysabari may have a dampening effect on the immune system that encourages the formation of the potentially deadly skin cancer, the letter stated.
And now that Tysabri has been approved for people with Crohn's disease, more people may be at risk, although those with no family history of melanoma and no moles probably don't need to worry, Mullen said.
"Doctors should ask for a family history of melanoma and do a quick skin check," he said. "Tysabri isn't the only drug in our arsenal. You could give the patient something else if you were concerned about that."
The National Multiple Sclerosis Society has more on treatments for MS.
SOURCES: John Thomas Mullen, M.D., assistant professor, surgery, Harvard Medical School, and sur
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