Which type of malignancy is most likely to first present as a proximal biliary obstruction?

Pancreatic cancer is often associated with proximal biliary obstruction due to its anatomic location and the way it infiltrates surrounding structures. The head of the pancreas is located adjacent to the duodenum and the bile ducts. When a tumor arises in the head of the pancreas, it can directly compress, invade, or obstruct the common bile duct, leading to jaundice and other symptoms associated with biliary obstruction.

This is a common initial presentation in patients with pancreatic cancer, particularly in the presence of an adenocarcinoma, which is the most prevalent type of pancreatic cancer. The obstructive jaundice caused by this obstruction often leads to the diagnosis of pancreatic cancer as it prompts further imaging studies, such as ultrasound or CT scans, to identify the cause of the bile duct obstruction.

In contrast, while liver cancer and gallbladder cancer can also cause biliary obstruction, they do not typically present in the same manner as pancreatic cancer. Liver cancer often presents with hepatic symptoms or as a metastasis rather than directly causing obstruction. Gallbladder cancer can cause obstruction as well, but it may be less common to present first with proximal biliary obstruction compared to pancreatic tumors. Duodenal cancer might also present with biliary obstruction, but again,