Vinegar-induced Collection of Duodenal Pancreatic Juice Via Endoscopic Ultrasound

The goal of this clinical trial is to learn about the feasibility of collecting pancreatic juice through duodenal aspiration by ultrasound endoscopy (EUS) for molecular marker testing after intraduodenal infusion of vinegar in patients with suspected pancreatic cancer and who are scheduled to have endoscopic ultrasound with fine needle aspiration (EUS-FNA). The main questions it aims to answer are: * Is vinegar-induced collection of duodenal pancreatic juice via endoscopic ultrasound feasible? * What is the best operating condition (amount of vinegar, collection time, etc.) of vinegar-induced collection of duodenal pancreatic juice via endoscopic ultrasound? Participants will have EUS as scheduled, during which different amount of vinegar will be infused into duodenum and then pancreatic juice be collected for different time via suction by EUS. Researchers will compare the amount of collected pancreatic juice and molecular marker level in different groups to determine the best operating condition for vinegar-induced collection of duodenal pancreatic juice via endoscopic ultrasound.