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. Both companies’ boards have approved the transaction, which is expected to close in the second quarter. The deal is subject to a majority of Terns’ stockholders tendering their shares in a tender offer that will be initiated by a Merck subsidiary.