Ciulla Clinical Chemistry Practice Test 2026 - Free Clinical Chemistry Practice Questions and Study Guide

CA 19-9 is a sialylated Lewis antigen that serves as a tumor marker most closely linked to pancreatic cancer. It is produced by pancreatic and biliary tract epithelium and tends to be elevated in pancreatic ductal adenocarcinoma, making it useful for monitoring treatment response and checking for recurrence. However, it is not perfectly specific: levels can rise in other gastrointestinal cancers and in benign conditions like biliary obstruction or cholestasis. Additionally, a subset of people who are Lewis antigen negative do not produce CA 19-9 at all, which can lead to false-low results. Other markers listed are associated with different cancers (for example, CA 15-3 with breast cancer; CEA with colorectal and several others; CA 54-5 with breast cancer), leaving pancreatic cancer as the primary association for CA 19-9.