Shares of drugmaker Day One Biopharmaceuticals DAWN.O surge 65.9% to $21.20 premarket
French drugmaker Servier said it will buy co for about $2.5 billion
Servier to pay $21.50 per share of DAWN in cash, which represents a premium of 68% to stock's last close
As of last close, DAWN up 37.1% YTD