What is CA125

Last Modified: November 1, 2001

Dear OncoLink "Ask the Experts,"
What is CA125?


CA125 is a substance which is found in very low levels in the human body. In recent years, CA125 has become a widely used tumor marker which is measured most often in women with cancers of the reproductive system including the uterus, fallopian tubes and ovaries. Other cancers that may cause abnormal CA125 levels include cancer of the pancreas, lungs, breast and colon. CA 125-II, an improved version of the original CA 125 assay, is now commercially available.

What is a tumor marker?  
Researchers have identified certain markers which seem to correlate with the presence of particular types of cancer. A tumor marker can be detected in the blood or other body fluids and may be an indicator of cancer cell production. It is important to note, however, that no individual tumor marker is conclusive for cancer and virtually all are present at low levels in the normal human body or in other non-cancerous conditions. For example, CA125/CA125-II can be elevated during menstruation, pregnancy or in individuals with ovarian cysts, pericarditis, hepatitis, cirrhosis of the liver or peritonitis, an infection of the lining of the abdomen.

What is a normal CA125/CA125-II level?  
Laboratory "normal ranges" for a blood level of CA-125 may vary. Most labs use under 35u/ml . Although some labs will use under 45u/ml . If you have concerns about your CA-125 please consult your physician.

What does an elevated CA125/CA125-II level mean?  
Many things can cause an elevation in an individual's CA125/CA125-II level. During menstruation and the first trimester of pregnancy, CA125/CA125-II levels rise in some women, especially those with a history of endometriosis. Ovarian cysts, pericarditis, hepatitis, cirrhosis of the liver or peritonitis, an infection of the lining of the abdominal cavity, can also cause elevated levels of CA125/CA125-II. Overall, elevated CA 125/CA125-II levels can be found in 1-2% of healthy individuals and in patients with nonmalignant conditions as listed above.

Certain cancers have been associated with abnormal CA125/CA125-II levels. Most commonly, elevated CA125/CA125-II levels have been identified in women with cancers of the reproductive system, including the uterus, fallopian tubes and ovaries. Cancer of the pancreas, lungs, breast and colon also may cause abnormal CA125/CA125-II levels.

Once a cancer is diagnosed, CA125/CA125-II levels may prove to be an effective indicator of the effectiveness of cancer treatment. A declining CA125/CA125-II value may indicate a good response to treatment and a favorable prognosis. Persistently rising CA125/CA125-II levels may be associated with a growing tumor, presence of tumor on the peritoneum that lines the abdomen or a recurrence of a previously treated tumor. As such, rising CA125/CA125-II levels during or after treatment often indicate a poor therapeutic response and an unfavorable prognosis. An increase in the CA125/CA125-II value may occur as much as 3 to 4 months before the presence of a tumor can be detected by other means.

Although CA125/CA125-II levels often rise and fall in connection with cancer progression or regression and thus may offer some indication of the response of a tumor to therapy, in many patients with ovarian cancer the amount of CA125/CA125-II in the blood is not related to tumor size and cannot serve as a guide to tumor response to different treatments. Furthermore, in all cases and with all types of tumors, normal CA125/CA125-II levels do not necessarily rule out continued cancer growth, recurrence of cancer, or the presence of extensive disease. Additional evaluation is necessary to make such determinations.

How are CA125/CA125-II levels monitored?  
CA125/CA125-II levels are detected through analysis of a blood sample, drawn in the same manner as other routine blood tests.

How often are CA125/CA125-II levels checked?  
A patient's physician will determine the frequency for monitoring CA125/CA125-II levels during and after cancer treatment. The type of cancer, tumor size, patient's baseline CA125/CA125-II level and type of treatment will affect the frequency of CA125/CA125-II monitoring.

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