In June 2013, Gordon Cornwall's melanoma went metastatic and spread to his brain. He and his wife, Claudia, thought it was "game-over." But his oncologist encouraged them to look for a clinical trial that might work for his form of melanoma. After embarking on a continent-wide search, they found a study in Texas with spots for just two more patients. They scrambled to get Gordon enrolled, and in August 2013, three days after he had his first infusion,...