Immunohistochemistry
Immunohistochemistry (IHC) is a method of analyzing and identifying cell types based on the binding of antibodies to specific components of the cell. IHC is used to diagnose the type of cancer and to help determine the patient's prognosis. In cases such as metastases or carcinoma of unknown origin, where it may be difficult to determine the type of cell from which the tumor originated, immunohistochemistry can identify cells by the characteristic markers on the cell surface. IHC can also help distinguish between benign and malignant tumors. Immunohistochemistry requires a sample of tissue from a biopsy; usually the tissue sample is examined fresh, but frozen or chemically preserved material can be used. A blood sample or bone marrow may also be examined.
Preparation
The tissue sample is sliced extremely thinly, so that it is approximately one cell thick, then the sample is fixed onto a glass slide. The tumor cells in the sample have characteristic markers, or antigens, on their cell surfaces which can be used to help identify the specific type of tumor cell. Antibodies against these characteristic antigens are added to the sample on the slide, and the antibodies bind wherever the antigens are present. Excess antibody is then washed away. The antibodies that remain bound to the cell have labels on them that either fluoresce (glow) or undergo a chemical reaction that makes them visible by microscope. The pathologist is able to see the specially labeled tumor antigens as they appear in the patient's tissue, leading to the identification of the cell type, and thus origin of the tumor.
Description of Test Results
Normal
Normal results will simply look like normal cells. The cells will have a high level of maturity and be located only in sites appropriate to their cell type. For example, analysis of lymph nodes will show only the cells that belong there, not cells that would normally be present in the breast. No specific tumor antigens will be present in increased numbers.
Abnormal
An abnormal result would consist of cells which appear immature or poorly differentiated, or that are found in an inappropriate tissue for their cell type. The pathologist may test for the presence of a particular antigen, such as Ki-67, carcinoembryonic antigen (CEA), or prostate specific antigen (PSA). In this case, there may be a numerical standard value to compare normal to abnormal results and help the physician in determining prognosis.
