MELVILLE, NY ( TheStreet) -- Japanese drug maker Astellas has launched a $3.5 billion hostile tender offer for U.S. biotech firm OSI Pharmaceuticals ( OSIP), maker of the lung cancer drug Tarceva.

Astellas is seeking to acquire all outstanding shares of OSI Pharma for $52 a share, representing a 40% premium over OSI Pharma's Friday closing price of $37.02, Astellas announced Monday.

The hostile tender offer for OSI Pharma comes after numerous previous entreaties by Astellas to buy the U.S. drugmaker were spurned, Astellas said in a statement.

"This offer follows our attempts over the past 13 months to engage OSI in meaningful discussions. We firmly believe in the compelling strategic rationale behind the combination and the opportunity it provides to the OSI stockholders to realize full and fair value, in cash, immediately," said Masafumi Nogimori, president and CEO of Astellas, in a statement.

Sales of OSI Pharma's lung cancer drug Tarceva rose 17% to $1.2 billion in 2009. Tarceva is co-marketed by the Swiss drug giant Roche/Genentech.

Last year, Astellas launched an unsuccessful and hostile tender offer for U.S. drugmaker CV Therapeutics, which was ultimately acquired by Gilead Sciences ( GILD).

-- Reported by Adam Feuerstein in Boston.

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