What Are Cancer Markers in a Blood Test?

Cancer markers, usually referred to as tumor markers, are substances produced by cancerous cells or benign tumors, as defined by the National Cancer Institute. In some cases, healthy tissues also produce tumor markers in response to the presence of cancerous cells.

Tumor markers are found in the bodily fluids and tissues of some people who have cancer, states the National Cancer Institute. The presence of a tumor marker in the blood does not necessarily mean a person has cancer. It is also possible to have cancer without having elevated levels of a tumor marker for that particular cancer. Tumor marker testing may be done in conjunction with tissue biopsies to ensure an accurate diagnosis.

Tumor markers are often used to determine if a patient is responding to cancer treatment, reports the National Cancer Institute. If the amount of tumor marker in the blood decreases, it is usually a sign the cancer is responding to treatment. If the tumor marker level increases or stays the same, the cancer may not be responding.

As of January 2015, more than 20 tumor markers have been identified, according to the National Cancer Institute. CA 19-9, CA-125 and AFP are three of the tumor markers used clinically, reports Lab Tests Online.. CA 19-9, or cancer antigen 19-9, is associated with cancers of the pancreas, colon, bile duct, stomach and gallbladder. CA-125 is the tumor marker used to detect and manage ovarian cancer. The AFP tumor marker may be elevated in cases of ovarian, testicular or liver cancer.