WASHINGTON - Federal regulators are investigating whether a group of best-selling arthritis drugs heighten the risk of cancer in youngsters.

The Food and Drug Administration said yesterday that it had received 30 reports of children and young adults developing cancer while taking the drugs over the last 10 years. Roughly half the cases were lymphomas, a type of immune-system cancer. Others reported were leukemia, melanoma, and cancers of various organs.

The drugs under review include Abbott Laboratories' Humira, Schering-Plough's Remicade, and Enbrel, which is marketed by Amgen and Wyeth. They are prescribed to children with arthritis to block a chemical that causes inflammation. The drugs also are used to treat children with the intestinal disorder Crohn's disease.

The products, known as tumor necrosis factor blockers, are key revenue drivers for the companies. Humira was Abbott's best-selling product last year with more than $3 billion in sales. Remicade topped Schering-Plough's portfolio with sales of $1.65 billion.

The safety of Humira was reviewed in February when the FDA first cleared it for use in juvenile arthritis, Abbott said in a statement. The company has not recorded any instances of lymphoma in children.

Representatives of the other companies did not immediately return calls for comment.

The FDA said the drugs' labeling already warns of a potential association with cancer, but the agency's investigation will focus on risks to younger patients.

The statement posted on the FDA's Web site said it will take long-term studies to definitively assess the drugs' safety risks since cancers take years to develop.

The Belgian drugmaker UBC is conducting a long-term study of risks, including cancer, with its drug Cimizia, which is part of the medication class. But the FDA said that study would not be complete until 2019.

The agency has asked drugmakers to provide all information about children who developed cancer while taking the medications. Regulators will report the findings of their review by November.

Doctors should consider the risks of cancer when considering prescribing the drugs for youngsters, the FDA said.