Mucicarmine is a special stain test (using a colouring stain) performed by pathologists to look for a type of protein called mucin. Mucin is made by specialized epithelial cells and it helps protect cells from damage. Mucin-producing cells are very common in the digestive tract (notably the colon) and the respiratory tract (notably the lungs). Pathologists perform this test when they are trying to determine if the cells they are looking at are producing mucin. When the slide is examined under the microscope, intracellular mucin (mucin inside of the cell) appears pink or red. Intracellular mucin is commonly found in a type of cancer called adenocarcinoma and this test can help pathologists tell the difference between adenocarcinoma and other types of cancer that do not show intracellular mucin.