UPDATE 2-Regeneron, Sanofi drug fails against pancreatic cancer

* Companies say drug deemed ineffective in Phase III study

* Studies of aflibercept continue vs other cancer types

* Regeneron stock down about 5 pct (Adds details on failed study, studies that continue)

NEW YORK, Sept 11 (Reuters) - Sanofi-Aventis (SASY.PA) and Regeneron Pharmaceuticals (REGN.O) on Friday said they had halted the trial of a drug for treatment of pancreatic cancer because it was not effective, but would continue studies of the drug to treat other cancers.

Shares of Regeneron, a biotechnology company based in Tarrytown, New York, fell almost 5 percent in after-hours trading, from their closing price on Friday of $21.88 on the Nasdaq. Paris-based Sanofi (SNY.N) shares were unchanged in after-hours activity, from their close on Friday of $35.05 on the New York Stock Exchange.

The companies said an independent data monitoring committee had determined that aflibercept in combination with a standard drug called gemcitabine would be unable to prolong survival beyond that seen with gemcitabine alone.

Patients enrolled in the late-stage trial had pancreatic cancer that had spread to other parts of the body and were taking the combination of drugs as a first-line treatment, meaning they had not previously been treated for the cancer.

The companies noted that pancreatic cancer is among the most difficult-to-treat cancers and that other experimental drugs have failed to significantly improve outcomes beyond those seen with existing treatments.

They said ongoing Phase III trials of aflibercept will continue against metastatic colorectal cancer, metastatic prostate cancer and non-small cell lung cancer. (Reporting by Ransdell Pierson; Editing by Carol Bishopric)