Final answer:
The tumor marker that can be used to follow pancreatic cancer is CA19-9.
Step-by-step explanation:
The tumor marker that can be used to follow pancreatic cancer is CA19-9. CA19-9 is a cancer-specific marker that is related to the presence of pancreatic cancer tissue. It is not specific enough for making a diagnosis, but it can be useful in the follow-up of treated patients to describe the progress of the disease or response to treatment.