Shares of Gilead fell more than 9% on Monday after a key drug from the company did not significantly extend the lives of patients with a certain lung cancer in a late-stage trial.The results are a blow to Gilead, which is working to become a power player in the cancer space. The treatment, Trodelvy, is one of Gilead's best-selling cancer drugs, contributing roughly a third of its $769 million in oncology sales during the third quarter.The phase-three study is part of an effort to expand the use of Trodelvy, ...