Bristol Myers Squibb entered a definitive merger agreement to acquire RayzeBio, Inc. for approximately $4.1 billion.    RayzeBio is a clinical-stage radiopharmaceutical therapeutics (RPT) company with actinium-based RPTs and a pipeline of potentially first-in-class and best-in-class drug development programs. Current pipeline programs are targeting the treatment of solid tumors, including gastroenteropancreatic neuroendocrine tumors (GEP-NETs), small cell lung cancer, hepatocellular carcinoma ...