The CA 125 “tumor associated protein” or “tumor marker”


by Dr. C.H. Weaver M.D. updated 9/2019

What is a CA 125?

CA 125 is a “tumor associated protein” “bio-marker” or “tumor marker” that can be measured in the blood. It can provide useful information about the biological state of ovarian cancer. It is more accurately considered a “tumor associated protein than a “tumor marker” because elevated CA 125 levels do not always indicate the presence of cancer.

How is CA-125 measured?

CA 125 is measured in the laboratory from a simple blood sample. The reference range of CA 125 is 0-35 units/mL (0-35 kU/L). The cutoff of 35 kU/L for CA 125 was determined from the distribution of values in healthy individuals to include 99% of the normal population. If the CA 125 level is higher than normal, it may be due to a benign condition, or the test result could indicate the presence of ovarian, endometrial, peritoneal or fallopian tube cancer.

What does it mean if CA 125 is elevated above the normal range?

An elevated CA 125 may mean cancer is present however there are also a number of benign conditions that cause elevations of the CA 125 level. Pregnancy, endometriosis, uterine fibroids, pancreatitis, normal menstruation, pelvic inflammatory disease, and cirrhosis of the liver as well as benign tumors or cysts of the ovaries may cause an abnormal test result.

Does a high CA 125 always mean cancer?

No - CA 125 can be absent when cancer is present, and levels can be high when no disease or no malignant disease exists.

How is CA 125 used in the management of ovarian cancer?

The CA 125 test is used in 4 main ways;

· Screening: Ca 125 can be used to screen for ovarian, primary peritoneal and fallopian tube cancers in high-risk women, or in women with abnormal findings on examination or ultrasound but not in the population of normal women. CA 125 is not considered to be a screening test for the early detection of ovarian cancer.

· Monitoring: CA 125 can be used throughout the course of ovarian cancer treatment to monitor the effectiveness of treatment.

· Prognosis: CA 125 can predict treatment outcomes for some women with ovarian and closely related cancers, such as fallopian tube and primary peritoneal cancer.

· Detection: CA 125 is used to detect recurrent ovarian cancer in women who have been previously treated.

Does early treatment of a CA 125 recurrence improve outcomes?

The MRC OV05/EORTC 55955 clinical trial evaluated Women in remission after first-line treatment for ovarian cancer. When CA125 was > 2x the upper limit of normal women either started chemotherapy treatment or waited until there was an objective reason to begin treatment and directly compared. Early treatment of a rising CA125 was associated with a more rapid decline in quality of life and no improvement in survival when compared to delayed treatment.

Comments (24)
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David Doveson
David Doveson



It is important to understand what your CA-125 is and how it is used. The CA-125 is a sugar associated protein called a glycoprotein found in the blood. It is commonly referred to as a tumor marker because it provides information about a disease’s biological state and its level can be measured when obtained from the blood. However, to be more accurate from a scientific standpoint, it is considered a tumor associated protein. Why? Because an elevated CA-125 level does not always mean a woman has ovarian cancer. CA-125 levels can sometimes be misleading.


A novel tumor-associated protein (TAP), that was originally detected immunologically through the use of a monospecific antiserum against a placental antigen, was quantified by means of the rocket technique of Laurell.


Cancer cells spread to other parts of the body through the blood and lymph systems. There are more than 100 different types of cancers which are named for the organ or type of cell in which they appear e.g., lung cancer, colon cancer, breast cancer, prostate cancer, liver cancer and stomach cancer.


Cancer is the second leading cause of mortality in EU countries after the disease of the circulatory system. Cancer is responsible for +/- 26% of death causes in the EU. Lung cancer accounts for the greatest number of all cancer deaths, while breast cancer accounts for the highest number of cancer death in woman.

Ovarian Cancer