This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pancreas, Subject name: Surgery
[{'content': 'In carcinoma head of pancreas, nausea and vomiting is due to: \nSelect and explain. \nA. External compression of duodenum, B. Poal vein infiltration, C. Proliferation infiltration of tumor into duodenum, D. Chemotherapy related', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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.', 'role': 'assistant'}]