CA 19-9 has achieved a defined role in the diagnosis, prognosis, and monitoring of patients with pancreatic cancer. For diagnosis, a reference value above 200 u/mL in a nonjaundiced patient with a confirming CT scan has a very high predictive value. For prognosis, a low preoperative value and a normal value after resection predict a good outcome. Similarly, CA 19-9 levels have been used successfully in monitoring the response to neoadjuvant therapy.