Sanofi announced that it will buy pharma company Blueprint Medicines for $129 per share, making the deal worth more than $9 billion. Blueprint specializes in systemic mastocytosis and other diseases driven by KIT, a receptor on mast cells.

French drugmaker Sanofi said Monday it has agreed to acquire Blueprint Medicines for $9.5 billion, sending shares of the Cambridge, Mass.-based biopharma firm soaring in premarket trading.

France's Sanofi has agreed to buy U.S.-based Blueprint Medicines Corporation for up to $9.5 billion to boost its position in rare immunology diseases, in the biggest deal struck by a European healthcare company so far this year,