The CA-19.9 test is a key 'tumor marker' test used by specialists. It measures the level of a protein that can be elevated in patients with certain cancers, most notably pancreatic cancer. It is not a screening test for cancer in the general population. Its primary, critical use is for monitoring the effectiveness of cancer treatment (such as chemotherapy) and for checking for the recurrence of the disease in patients who have been diagnosed. This simple blood test provides your care team with the critical, actionable data needed to manage your health and guide your treatment journey.