Cancer antigen 125 (CA-125) is a substance produced by the fallopian tubes, the endometrium, and the lining of the abdominal cavity (peritoneum). See an illustration of the female reproductive system.

CA-125 is used as a tumor marker—an indicator of some types of cancer, especially ovarian cancer. The amount of CA-125 in a woman's blood and body fluids often increases when cancer of the ovaries is present. However, cancer antigen 125 is not used to screen for ovarian cancer because:

• Other conditions can also cause increased levels of CA-125, including pregnancy, menstruation, some non-ovarian cancers, and some noncancerous disorders.
• CA-125 levels do not rise above the normal range in all women who have ovarian cancer.
• CA-125 levels often do not rise until the cancer is in an advanced stage.

This test is done on a blood sample taken from a vein.

Cancer Antigen 125 (CA-125)
Results

Normal

Greater than normal values may mean

• High levels of CA-125 can indicate cancer of the ovaries or surrounding tissues (such as a endometrium). Other types of cancer that can cause an increase in CA-125 include cancer of the pancreas, stomach, esophagus, and liver. Smaller increases in CA-125 levels can be caused by breast, colon, or lung cancer.
• Most women with a detectable lump in the pelvic area who have ovarian cancer also have CA-125 values greater than 65 U/mL.
• Other diseases that may cause increased levels of CA-125 include pelvic inflammatory disease (PID), endometriosis, liver disease (hepatitis or cirrhosis), pancreatitis, and lupus.
• Pregnancy and menstruation can cause elevated blood levels of CA-125.