Immunohistochemistry

Definition

Immunohistochemistry is a method of analyzing and identifying cell types based on the binding of antibodies to specific components of the cell. It is sometimes referred to as immunocytochemistry.

Purpose

Immunohistochemistry (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 primary 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.

Description

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. 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.

The pathologist will try to assess the level of maturity of the tumor cells, which will help him to determine their origin. He will be checking for cell types that are found in an inappropriate part of the body, for example prostate cells in a lymph node. He will also look for cell characteristics that will indicate if the tumor is benign or malignant. Proteins involved in the replication of genetic material and cell growth may be present in greater amounts; for example, antibodies against the antigen Ki-67 are used to evaluate malignant melanomas, breast carcinomas, and non-Hodgkin's lymphomas . Hormone receptors may also be examined. The presence of receptors to estrogen and progesterone indicate a good prognosis for breast cancer patients. Pathologists may also look for an increase in tumor suppressor proteins. A wide variety of antibodies are available to help determine the origin of the tumor, whether it is growing rapidly, and whether it is a type of tumor that responds well to particular treatments.

Preparation

The physician will choose the type of sample to be taken based on the type of tumor. If the patient has a solid tumor, a tissue sample may be biopsied; if the entire tumor is being removed a biopsy may be taken during surgery. In this case the patient should prepare for the surgery or the biopsy as the physician suggests. A routine blood sample may also be required; in most cases, no additional preparation is required.

Aftercare

The only aftercare that might be required is from the sample collection process.

Risks

The risks associated with IHC are the risks associated with the sample collection, either the biopsy of the tumor or the drawing of blood. The only other concern is the possibility that the test could yield unclear results.

Normal results

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 results

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.

See Also Receptor analysis; Tumor markers

Resources

BOOKS

Javois, Lorette C. Immunocytochemical Methods and Protocols Totowa, NJ:Humana Press Inc., 1999.

Polak, J.M., and S. Van Noorden. Introduction to Immunocytochemistry New York: Springer-Verlag, 1997.

PERIODICALS

Bendayan, Moise. "Worth Its Weight in Gold." In Science 291 (16 February 2001): 1363-1365.

Cote, RJ et al. "Role of Immunohistochemical Detection of Lymph-Node Metastases in Management of Breast Cancer." In The Lancet 354:(11 September 1999): 896-900.

Elledge, Richard M. and C Kent Osborne. "Oestrogen Receptors and Breast Cancer." British Medical Journal 314:(28 June 1997): 1843-1845.

Gastl, Gunther et al. "Ep-CAM Overexpression in Breast Cancer as a Predictor of Survival." In The Lancet 356:(9 December 2000) 1981-1982.

Racquel Baert, M.S.

KEY TERMS

Antibody

—A protein formed by the immune system to react with a specific antigen.

Antigen

—Any protein that elicits a unique immune response.

Biopsy

—A sample of tissue taken from a tumor to compare with other normal tissue.

Histology

—The study of tissues.

QUESTIONS TO ASK THE DOCTOR

• What do you expect to learn from this test?
• What are the alternatives to this test?
• Are there any risks or complications?
• Are any special preparations required?
• Is hospitalization required?
• Is it possible that the test may give a false positive, a false negative, or unclear results?