Immunohistochemistry (IHC) is a process used to diagnose some types of cancer including mesothelioma. The procedure involves locating antigens in biopsy tissue through the use of a visual marker. Common markers include fluorescent dye, enzymes, colloidal gold and radioactive elements. If cellular events associated with cancerous tumors – such as an increase in cell death – are evident in the tissue, then the abnormal activity will be highlighted by the stained tissue sample. Immunohistochemistry cannot only help in the identification of a tumor, but it can also distinguish whether or not a tumor is benign or malignant.
The Immunohistochemistry Process
Immunohistochemistry begins with collection of a sample of tissue from the patient. The integrity of the sample tissue is paramount to the accuracy of the procedure. Fresh tissue samples are hence typically examined as soon as possible. However, frozen or preserved tissue samples may be used in some cases.
The sample is sliced thinly to achieve a one-cell thickness and placed on a glass slide. The sample is then introduced to antibodies, which bind to antigens in the cell. A microscope is used to locate these bound antibodies, which are visible either through fluorescence or chemical reactions.
Based on the binding patterns present in the immunohistochemistry tissue sample, pathologists can glean an enormous amount of information. For example, the process allows experts to determine the origin of the abnormal cells, which often leads to a successful diagnosis.
Two immunohistochemistry methods are employed – direct and indirect. The direct IHC method is a straightforward one-step process that creates a direct reaction between the antigen and the labeled antibody. This method is nicely simple but is less sensitive than the more complex indirect method. For this reason, the direct method is rarely used today.
The indirect method requires the use of two antibodies – a primary unlabeled antibody and a secondary labeled antibody. The addition of the primary antibody allows for signal amplification of the process, which in turn delivers improved sensitivity and more accurate results.
Immunohistochemistry has been a successful technique for marking antigens since the early 1940s. In comparison to similar investigative cell techniques, IHC provides improved precision in locating specific proteins of interest associated with the identification of cancerous tumors. For example, studies have shown that IHC is more sensitive in the diagnosis of breast cancer when compared to alternative tests such as biochemical determination and dextran-coated charcoal assay (DCC). Immunohistochemistry is also invaluable in allowing doctors to distinguish between adenocarcinoma and malignant mesothelioma.
Related: Problems in mesothelioma diagnosis. – Abstract of study conducted by British scientists.