Medivation Inc. broadened its cancer drug portfolio in a low-risk deal with a $5 million upfront payment and an escape hatch. The San Francisco company , which developed the prostate cancer drug Xtandi with Astellas Pharma Inc., said Friday that it licensed exclusive worldwide rights to an immune system-modulating drug from CureTech Ltd. So-called immuno-oncology drugs, including "checkpoint inhibitors" that rev up patients' own immune systems to attack cancer, are a white-hot area of cancer drug development.