In this advanced endoscopic technique, a scope with an ultrasound transducer at its tip examines beyond the walls of the esophagus, stomach, small bowel, and colorectum. It can be used for therapeutic or diagnostic purposes. It is used to diagnose, stage, and biopsy cancers, as well as drain cysts and fluid collections. It is also used to block nerves that cause intense pain in advanced pancreatic cancer.  In rare circumstances, it can also be used to drain the bile duct in patients with terminal duodenal or pancreatic cancer.