A lab test that uses antibodies to test for certain antigens (markers) in a sample of cells. The antibodies are usually linked to an enzyme or a fluorescent dye. When the antibodies bind to the antigen in the cell sample, the enzyme or dye is activated, and the antigen can then be seen under a microscope. Immunocytochemistry is used to help diagnose diseases, such as cancer. It may also be used to help tell the difference between different types of cancer.