In carcinoma head of pancreas, nausea and vomiting is due to:

Depending upon the location of the tumor, the symptoms may vary. - Periampullary carcinoma - at the ampulla; most common symptom is Jaundice. - Carcinoma at the head of pancreas - External compression of duodenum , compression of bile duct; most common symptom is jaundice. - Carcinoma at the body or tail of pancreas - asymptomatic at early stages. Most common symptom at later stages is weight loss. Due to involvement of retroperitoneal nerve plexus, there is abdominal pain. - When malignancy advances and infiltrates the 2nd pa of duodenum, it causes nausea, vomiting or gastric outlet obstruction.