Periampullary cancer refers to tumors that arise near the ampulla of Vater, where the bile duct and pancreatic duct meet and empty into the small intestine. It includes cancers of the pancreas, bile duct, duodenum, and ampulla. These cancers often present with early symptoms like jaundice, offering a better prognosis than pancreatic cancer. Diagnosis involves imaging and biopsy, and treatment typically includes surgery, chemotherapy, or radiation, depending on the stage.