In late 2015, Bob Minetti started feeling stomach pains that mysteriously came and went and moved to his lower back. Extensive testing led to one of the most dire of diagnoses: pancreatic cancer. And the small tumor was lodged against a key blood vessel, so it couldn't be surgically removed. Minetti, a retired academic fundraiser from South Natick, Massachusetts, enrolled in a clinical trial at Massachusetts General Hospital that included a powerful newer chemotherapy, called FOLFIRINOX. The tumor, which he thought of as about the size of a hard candy, responded dramatically. "It's really shrunk like butter in the microwave,"...