Mucin is a protein made by cells. It is used to make a thick fluid called mucus. Mucus is normally found in saliva and other substances throughout the body. When viewed under the microscope, mucin has a light blue or grey colour. A special stain called mucicarmine makes can be performed to highlight mucin inside cells.
Mucin can be produced by both normal and abnormal cells. Cancers that produce mucin are usually called adenocarcinomas. Some non-cancerous tumours can also produce large amounts of mucin.
Intracellular mucin is mucin that is inside the body of the cell. That tells your pathologist that the cell is making the mucin. A goblet cell is a special type of cell that holds a large amount of mucin within its cell body. Goblet cells are normally found in the small bowel and the colon.
Pathologists often use the presence of mucin in the tissue as evidence to support their diagnosis or to exclude conditions that do not produce mucin. When examining a cancer under the microscope, intracellular mucin is used to support the diagnosis of adenocarcinoma.
Extracellular mucin is mucin that is outside of cells. Pathologists sometimes describe a large area of extracellular mucin as a “pool”.