Carbohydrate antigen 19-9 (CA19-9), also known as sialyl-Lewis^A, is a tetrasaccharide which is usually attached to O-

glycan The terms glycans and polysaccharides are defined by IUPAC as synonyms meaning "compounds consisting of a large number of monosaccharides linked glycosidically". However, in practice the term glycan may also be used to refer to the carbohydrate ...

s on the surface of cells. It is known to play a role in cell-to-cell recognition processes. It is also a

tumor marker A tumor marker is a biomarker that can be used to indicate the presence of cancer or the behavior of cancers (measure progression or response to therapy). They can be found in bodily fluids or tissue. Markers can help with assessing prognosis, s ...

used primarily in the management of

pancreatic cancer Pancreatic cancer arises when cell (biology), cells in the pancreas, a glandular organ behind the stomach, begin to multiply out of control and form a Neoplasm, mass. These cancerous cells have the malignant, ability to invade other parts of ...

Structure

CA19-9 is the sialylated form of Lewis antigen^A. It is a tetrasaccharide with the sequence Neu5Acα2-3Galβ1-3 ucα1-4lcNAcβ.

Clinical significance

Tumor marker

Guidelines from the

American Society of Clinical Oncology The American Society of Clinical Oncology (ASCO) is a professional organization representing physicians of all oncology sub-specialties who care for people with cancer. Founded in 1964 by Fred Ansfield, Harry Bisel, Herman Freckman, Arnoldus G ...

discourage the use of CA19-9 as a screening test for cancer, particularly

. The reason is that the test may be falsely normal (

false negative A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test resu ...

) in many cases or abnormally elevated in people who have no cancer (

false positive A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test resu ...

) in others. The main use of CA19-9 is therefore to see whether a pancreatic tumor is secreting it; if that is the case, then the levels should fall when the tumor is treated, and they may rise again if the disease recurs. Therefore it is useful as a surrogate marker for

relapse In internal medicine, relapse or recidivism is a recurrence of a past (typically medical) condition. For example, multiple sclerosis and malaria often exhibit peaks of activity and sometimes very long periods of dormancy, followed by relapse or r ...

. In people with pancreatic masses, CA19-9 can be useful in distinguishing between cancer and other diseases of the gland.

Limitations

CA19-9 can be elevated in many types of gastrointestinal cancer, such as

colorectal cancer Colorectal cancer (CRC), also known as bowel cancer, colon cancer, or rectal cancer, is the development of cancer from the Colon (anatomy), colon or rectum (parts of the large intestine). Signs and symptoms may include Lower gastrointestinal ...

esophageal cancer Esophageal cancer (American English) or oesophageal cancer (British English) is cancer arising from the esophagus—the food pipe that runs between the throat and the stomach. Symptoms often include dysphagia, difficulty in swallowing and weigh ...

and

hepatocellular carcinoma Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer in adults and is currently the most common cause of death in people with cirrhosis. HCC is the third leading cause of cancer-related deaths worldwide. HCC most common ...

. Apart from cancer, elevated levels may occur in

pancreatitis Pancreatitis is a condition characterized by inflammation of the pancreas. The pancreas is a large organ behind the stomach that produces digestive enzymes and a number of hormone A hormone (from the Ancient Greek, Greek participle , "se ...

cirrhosis Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, chronic liver failure or chronic hepatic failure and end-stage liver disease, is a chronic condition of the liver in which the normal functioning tissue, or parenchyma, is replaced ...

, and diseases of the bile ducts. It can also be elevated in people with obstruction of the

bile duct A bile duct is any of a number of long tube-like structures that carry bile, and is present in most vertebrates. The bile duct is separated into three main parts: the fundus (superior), the body (middle), and the neck (inferior). Bile is requ ...

s. In people who lack Lewis antigen^A (a blood type antigen on

red blood cell Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cel ...

s), which is about 10% of the white population, CA19-9 is not produced by any cells, even in those with large tumors. This is because of a deficiency of a

fucosyltransferase A fucosyltransferase is an enzyme that transfers an L-fucose sugar from a GDP-fucose (guanosine diphosphate-fucose) donor substrate to an acceptor substrate. The acceptor substrate can be another sugar such as the transfer of a fucose to a core ...

enzyme that is needed to produce Lewis antigen^A.

History

CA19-9 was discovered in the serum of patients with

colon cancer Colorectal cancer (CRC), also known as bowel cancer, colon cancer, or rectal cancer, is the development of cancer from the colon or rectum (parts of the large intestine). Signs and symptoms may include blood in the stool, a change in bowel ...

and

in 1981. It was characterized shortly after, and it was found to be carried primarily by

mucins Mucins () are a family of high molecular weight, heavily glycosylation, glycosylated proteins (glycoconjugates) produced by epithelial tissues in most animals. Mucins' key characteristic is their ability to form gels; therefore they are a key com ...

References

External links

* * CA19-9 a
Lab Tests Online

CA19-9: analyte monograph
- The Association for Clinical Biochemistry and Laboratory Medicine
Essentials of Glycobiology 3rd Edition, Chapter 14: "Structures Common to Different Glycans" https://www.ncbi.nlm.nih.gov/books/NBK453042/#_Ch14_s2_
{{Tumor markers Amino sugars Tetrasaccharides Acetamides Tumor markers Pancreatic cancer