Pfizer has clinched the purchase of US cancer drug company Medivation in a deal valued at about $14bn, (€12.4bn) adding blockbuster prostate cancer drug Xtandi to its portfolio.

Sanofi says it has sent a letter to Medivation’s board, urging the company to engage in negotiations regarding the French drugmaker’s unsolicited $9.3bn (€8.1bn) takeover offer and threatening to go directly to shareholders if talks don’t begin.