NEW YORK (Reuters) - Bristol-Myers Squibb Co (BMY.N: Quote, Profile, Research) and Medarex Inc (MEDX.O: Quote, Profile, Research) said on Friday they will delay seeking approval of their experimental treatment for advanced melanoma after U.S. health regulators set a higher-than-expected bar on the biotechnology drug.

Medarex shares fell more than 12 percent in after-hours trading.

The companies said the Food and Drug Administration is seeking additional overall survival data to further demonstrate the benefit of ipilimumab.

As a result the companies will not submit an approval application on ipilimumab this year, they said.

Bristol-Myers and Medarex said they are in discussion with the FDA about changing the main goal of an ongoing pivotal clinical trial of the drug to the tougher to achieve overall survival from the original end point of progression-free survival.

Progression-free survival is a measure of how long a patient goes without tumor growth or worsening of symptoms, while overall survival measures actual extension of life.

The companies said they remain committed to the development of ipilimumab, which also is being tested for prostate and lung cancer.

Ipilimumab is a fully human antibody that binds to a molecule on T-cells that plays a critical role in regulating natural immune responses to disease.

Shares of Medarex, which is far more dependent on ipilimumab than is Bristol-Myers, fell to $7.01 in extended trading from their Nasdaq close at $8.01.

(Reporting by Bill Berkrot; editing by Carol Bishopric)