Pfizer is to acquire cancer drug company Medivation in a deal valued at about US$14bn.
Medivation is best known for cancer treatment Xtandi, which it jointly markets with Japanese drug maker Astellas Pharma.
Pfizer will pay $81.50 per Medivation share, which is a 21% premium on the biotech firm's closing price of $67.19.
The boards of both companies have approved the deal, which is expected to close in the third or fourth quarter.
Pfizer chairman Ian Read said: "The proposed acquisition of Medivation is expected to immediately accelerate revenue growth and drive overall earnings growth potential for Pfizer.
"This transaction is another example of how we are effectively deploying our capital to generate attractive returns and create shareholder value."
Pfizer added that Medivation also has a promising pipeline of cancer drugs in late-stage clinical development, including the potential breast cancer treatment talazoparib and a lymphoma drug.
The deal comes last month after Medivation rejected a $9.3bn takeover bid from the French drug maker Sanofi, saying that offer, worth $52.50 per share, undervalued the company.
According to its website, Pfizer employs approximately 3,200 people in six sites across Ireland.