Mylan Inc. (MYL) has applied for U.S. regulatory approval to sell a generic version of Pfizer Inc.'s (PFE) Sutent cancer pill by challenging several patents on the drug.

In a regulatory filing Thursday, Pfizer said Mylan had notified it of the challenge earlier this month. Mylan is challenging "on various grounds" the Sutent basic patent, which expires in 2021, and two other patents that expire in 2020 and 2021, Pfizer said.

Last month, the Food and Drug Administration disclosed on its Web site that a company submitted an application to market generic Sutent, although the identify of the challenger wasn't known.

Sutent has been one of Pfizer's few successful new drugs in recent years, generating $964 million in sales last year. Launched in the U.S. in 2006, Sutent is approved to treat kidney cancer and certain gastrointestinal tumors.

Being first to file a patent challenge, called a "Paragraph IV" challenge, can be lucrative for a generic drug maker because it provides 180 days of exclusivity if the move is successful.

Even if Mylan succeeds, a generic version of the drug likely wouldn't make it to the market for years. Under the law, if a patent owner sues a generic applicant for infringement within 45 days of that notice, approval of the generic is stayed for 30 months.

The automatic 30-month stay allows time for resolution of the litigation, while protecting the patent holder from harm that could ensue from the FDA granting marketing approval to a potentially infringing product.

Officials from Mylan weren't immediately available for comment.

Pfizer shares closed down 2% at $16.56 Thursday, and were up three cents after hours.

-By Thomas Gryta, Dow Jones Newswires; 212-416-2169; thomas.gryta@dowjones.com

(Peter Loftus contributed to this article.)
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