An 80-year-old man has increasing jaundice with abdominal pain for the past 2 weeks. He has lost 4 kg over the past 5 months. On physical examination, there is the tenderness with palpable gallbladder in the right upper quadrant. An abdominal CT scan shows gallbladder and common bile duct dilation, along with a 3-cm mass in the head of the pancreas. Which of the following lesions is the most likely precursor to this mass?

He is most likely to have pancreatic adenocarcinoma. Diagnosis at the stage of pancreatic intraepithelial neoplasia (PanIN) is nearly impossible. The dilated palpable gallbladder represents the Courvoisier sign from obstruction of the biliary tree by a neoplasm. Despite this sign, cancer has had time to invade and is unlikely to be cured, so the prognosis of pancreatic adenocarcinoma is poor. However, there are chemotherapy agents and biologic monoclonal therapies that may slow cancer and prolong survival. This solitary mass is unlikely to be a metastasis. Primary carcinomas arising in the small intestine are rare. Neuroendocrine tumors that may arise from islets of Langerhans are often benign when small, and they do not transform into adenocarcinomas. Serous cystadenomas of the pancreas are nearly all benign, and likely to be cystic.