CA-125
Encyclopedia
CA-125 also known as mucin 16 or MUC16 is a protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that in humans is encoded by the MUC16 gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

. MUC16 is a member of the mucin
Mucin
Mucins are a family of high molecular weight, heavily glycosylated proteins produced by epithelial tissues in most metazoans. Mucins' key characteristic is their ability to form gels; therefore they are a key component in most gel-like secretions, serving functions from lubrication to cell...

 family glycoprotein
Glycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...

s. CA-125 has found application as a tumor marker
Tumor marker
A tumor marker is a substance found in the blood, urine, or body tissues that can be elevated in cancer, among other tissue types. There are many different tumor markers, each indicative of a particular disease process, and they are used in oncology to help detect the presence of cancer...

 or biomarker that may be elevated in the blood of some patients with specific types of cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...

s, or other benign conditions.

Structure and function

Mucin 16 is a membrane associated mucin that possesses a single transmembrane domain. MUC16 is a component of the ocular surface (including the cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...

 and conjunctiva
Conjunctiva
The conjunctiva covers the sclera and lines the inside of the eyelids. It is composed of rare stratified columnar epithelium.-Function:...

) and the respiratory tract and female reproductive tract epithelia
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...

. Mucin 16 plays a role as a lubricating barrier against foreign particles and infectious agents on the surface of epithelial cells. The expression of mucin 16 has been shown to be altered in dry eye
Keratoconjunctivitis sicca
Keratoconjunctivitis sicca , also called keratitis sicca, xerophthalmia or dry eye syndrome is an eye disease caused by eye dryness, which, in turn, is caused by either decreased tear production or increased tear film evaporation. It is found in humans and some animals...

.

As a biomarker

CA-125 is clinically approved for following the response to treatment and predicting prognosis after treatment. It is especially useful for detecting the recurrence of ovarian cancer
Ovarian cancer
Ovarian cancer is a cancerous growth arising from the ovary. Symptoms are frequently very subtle early on and may include: bloating, pelvic pain, difficulty eating and frequent urination, and are easily confused with other illnesses....

. Its potential role for the early detection of ovarian cancer is controversial and has not yet been adopted for widespread screening efforts in asymptomatic women. The key problems in using the CA-125 test as a screening tool are its lack of sensitivity and its inability to detect early stage cancers. An operation would be necessary to confirm that a woman with elevated CA-125 has ovarian cancer, with the associated risk of death from major surgery. In addition, even if cancer was confirmed in such circumstances, it usually would be at an advanced stage where therapy is less effective. The goal of many cancer biologists is to develop a test that would be employed to diagnose ovarian cancer at an early stage, when the effects of therapeutic interventions are optimal.

In April 2011 the UK's National Institute for Health and Clinical Excellence
National Institute for Health and Clinical Excellence
The National Institute for Health and Clinical Excellence is a special health authority of the English National Health Service , serving both English NHS and the Welsh NHS...

 (NICE) recommended that women with symptoms that could be caused by ovarian cancer should be offered a CA-125 blood test. The aim of this guideline is to help diagnose the disease at an earlier stage, when treatment is more likely to be successful. Women with higher levels of the marker in their blood would then be offered an ultrasound scan to determine whether they need further tests.

Specificity and sensitivity

It is best known as a marker for ovarian cancer
Ovarian cancer
Ovarian cancer is a cancerous growth arising from the ovary. Symptoms are frequently very subtle early on and may include: bloating, pelvic pain, difficulty eating and frequent urination, and are easily confused with other illnesses....

, but it may also be elevated in other cancers, including endometrial cancer
Endometrial cancer
Endometrial cancer refers to several types of malignancies that arise from the endometrium, or lining, of the uterus. Endometrial cancers are the most common gynecologic cancers in the United States, with over 35,000 women diagnosed each year. The incidence is on a slow rise secondary to the...

, fallopian tube cancer
Fallopian tube cancer
Primary fallopian tube cancer , often just tubal cancer, is a malignant neoplasm that originates from the fallopian tube.-Frequency:...

, lung cancer
Lung cancer
Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. If left untreated, this growth can spread beyond the lung in a process called metastasis into nearby tissue and, eventually, into other parts of the body. Most cancers that start in lung, known as primary...

, breast cancer
Breast cancer
Breast cancer is cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas...

 and gastrointestinal cancer
Gastrointestinal cancer
Gastrointestinal cancer refers to malignant conditions of the gastrointestinal tract, including the esophagus, stomach, biliary system, pancreas, bowels, and anus. The symptoms relate to the organ affected, and can include obstruction , abnormal bleeding, or other associated problems...

. CA-125 may also be elevated in a number of relatively benign conditions, such as endometriosis
Endometriosis
Endometriosis is a gynecological medical condition in which cells from the lining of the uterus appear and flourish outside the uterine cavity, most commonly on the ovaries. The uterine cavity is lined by endometrial cells, which are under the influence of female hormones...

, several diseases of the ovary, and pregnancy. It also tends to be elevated in the presence of any inflammatory condition in the abdominal area, both cancerous and benign.

Thus, CA-125 is not perfectly specific for cancer nor is it perfectly sensitive since not every patient with cancer will have elevated levels of CA-125 in the blood. For example, 79% of all ovarian cancers are positive for CA-125, whereas the remainder do not express this antigen at all.

Ranges in ovarian cancer

While this test is not generally regarded as useful for large scale screening by the medical community, a high value may be an indication that the woman should receive further diagnostic screening or treatment. Normal values range from 0 to 35 (U/mL). Elevated levels in post-menopausal women are usually an indication that further screening is necessary. In pre-menopausal women, the test is less reliable as values are often elevated due to a number of non-cancerous causes, and a value above 35 is not necessarily a cause for concern.

Discovery

ca 125 is a serum marker of
CA-125 was initially detected using the monoclonal antibody designated OC125. Dr.s Robert Bast, Robert Knapp and their research team first isolated this monoclonal antibody in 1981.

External links

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