The complaints concern Celgene's breast cancer drug Abraxane and Novartis's cancer drug Gleevec.

The Food and Drug Administration posted separate letters to each company on its website on Wednesday, asking them to stop using advertising that violates FDA guidelines.

The FDA inspects companies' marketing materials to make sure they do not illegally promote drugs for uses other than those approved by the agency, or make false claims that are not backed by clinical data.

For Celgene, the FDA said it also broadened the uses for Abraxane and omitted safety information in a paper displayed at the American Society of Clinical Oncology meeting in 2010.

Celgene spokesman Greg Geissman said the paper was produced and distributed by Abraxis, the original manufacturer of Abraxane. Celgene acquired Abraxis later in 2010.

"Celgene has never distributed the paper, and it has been discontinued from use," Geissman said. "We are working with (the FDA) to rectify all their concerns."

For Novartis, the FDA focused on a "Case Highlights" document that described how well Gleevec worked for a particular patient. The FDA said this was misleading because the document implied the drug would work just as well for other patients.

"A selected case study of one patient's treatment response does not constitute substantial evidence," the FDA said in the letter.

Novartis said that it had responded to the FDA's letter, but the company did not divulge the nature of its response.

(Reporting by Anna Yukhananov; Editing by Gerald E. McCormick and Steve Orlofsky)

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