Astellas Pharma has announced that it extended its all-cash tender offer for OSI Pharmaceuticals to 12:00 midnight New York City time yesterday.

The tender offer was previously set to expire at 5:00pm New York City time on Monday May 17, 2010.

Astellas Pharma had previously entered into a confidentiality agreement with OSI Pharmaceuticals, whereby OSI would provide certain non-public information that will provide Astellas with firmer ground, from which to launch a fresh takeover bid.

The agreement came after Japan’s Astellas agreed to not pursue any further OSI shares until 15 May, creating a standstill period of six weeks as opposed to the two years OSI had originally wanted.

In connection with the execution of a merger agreement with OSI Pharmaceuticals, Astellas increased the price it was offering to acquire all shares of common stock of OSI Pharmaceuticals, Inc., from $52.00 to $57.50 per share.