In a series, the New York Times profiles the work of Keith Flaherty, an oncologist at the University of Pennsylvania, who has evangelized a targeted approach to treating cancer. The first part follows the highs and lows of clinical trials after Flaherty jumped headlong into testing drugs targeting B-RAF mutations in cancer. His first drug from Bayer failed and finding the proper does for a second from Plexxikon has taken a few re-formulations, but holds a glimmer of promise: he has his first responder.