Carbohydrate antigen 19-9 (CA19-9), also known as sialyl-Lewis^A, is a

tetrasaccharide A tetrasaccharide is a carbohydrate which gives upon hydrolysis four molecules of the same or different monosaccharides. For example, stachyose upon hydrolysis gives one molecule each of glucose and fructose and two molecules of galactose Gala ...

which is usually attached to O- glycans 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 found in blood, urine, or body tissues that can be elevated by the presence of one or more types of cancer. There are many different tumor markers, each indicative of a particular disease process, and they are used in ...

used primarily in the management of pancreatic cancer.

Structure

CA19-9 is the sialylated form of Lewis Antigen^A. It is a

with the sequence Neu5Acα2-3Galβ1-3 ucα1-4lcNAcβ.

Clinical significance

Tumor marker

Guidelines from the American Society of Clinical Oncology discourage the use of CA19-9 as a screening test for cancer, particularly pancreatic cancer. 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 resul ...

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

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 resul ...

). 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 ...

. 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, esophageal cancer and hepatocellular carcinoma. 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 hormones. There are two main types: acute pancreatitis, and chronic pancr ...

cirrhosis Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, and end-stage liver disease, is the impaired liver function caused by the formation of scar tissue known as fibrosis due to damage caused by liver disease. Damage causes tissue rep ...

, 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. Bile is required for the digestion of food and is secreted by the liver into passages that carry bile toward the hepatic duct. It ...

s. In patients who lack the

Lewis antigen The Lewis antigen system is a human blood group system. It is based upon two genes on chromosome 19: FUT3, or Lewis gene; and FUT2, or Secretor gene. Both genes are expressed in glandular epithelia. FUT2 has a dominant allele which codes for an e ...

A (a blood type antigen on

red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

s), which is about 10% of the Caucasian 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 G ...

enzyme that is needed to produce Lewis antigen A.

History

CA19-9 was discovered in the serum of patients with colon cancer and pancreatic cancer 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 glycosylated proteins (glycoconjugates) produced by epithelial tissues in most animals. Mucins' key characteristic is their ability to form gels; therefore they are a key component in most ...

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