Pronunciation: (FY-brin)

A protein involved in forming blood clots in the body. It is made from the protein fibrinogen and helps stop bleeding and heal wounds. Sometimes fibrin-like substances may be found in higher than normal amounts in the blood and urine of patients with some types of cancer or other conditions. Measuring the amount of these substances may help to check how well cancer treatment is working or if the cancer has gotten worse. Fibrin is a type of tumor marker.

Source: NCI Dictionary of Cancer Terms