Merck is buying oncology company Terns Pharmaceuticals in a deal valued at approximately $6.7 billion as the pharmaceutical giant works on beefing up its cancer portfolio before a key patent on its cancer drug Keytruda expires in two years. Merck received accelerated approval for Keytruda from the Food and Drug Administration in September 2014 to treat advanced or unresectable melanoma. The drug has since been approved to treat more than 15 types of cancers and has been a key contributor to Merck's revenu ...