Immunohistochemistry in cancer diagnosis
In the pathological laboratory of a leading Israeli private hospital "Herzliya Medical Center," if necessary, immunohistochemical studies are performed.
What is the Immunohistochemistry (IHC), or Immunohistochemical Staining Methods?
The basis of the study by IHC is the antigen-antibody reaction and it is assessed not only a presence specific antigens/proteins on histological slices but also their location and quantity.
Biopsy or surgical specimens after additional fixing stages are embedded in paraffin for obtaining histological section; then, using a microtome, slices are prepared and placed on a histological glass.
Only after this procedure, serial staining can be done: at the end of each stage of staining the doctor-pathologist examines the slice using a microscope and decides whether the next phase of staining is necessary.
Fresh slices, as well as long-standing sections made from paraffin blocks for several years prior, are suitable for IHC.
The most common method of staining is an application of hematoxylin-eosin: the hematoxylin stains the cell nucleus in dark blue and the eosin stains the cell's cytoplasm in pink.
Demand for immunohistochemical studies to clarify the diagnosis grows every year. Moreover, the number of cases, as well as the quantity of biomarker tested in each case increase too.
What IHC is used for?
The direct objective of immunohistochemical staining is a characterization of cells in their immune profile. This assessment is essential in order to achieve further practical purposes: to clarify the diagnosis, to identify the source of metastasis (the tissue and / or organ with a primary tumor, an identification of the primary lesion), the differential diagnosis of Hodgkin's and non-Hodgkin's lymphoma, forecast the effectiveness of radiation or chemotherapy (including targeted drugs, as well as chemical and hormonal medicines). For example, in some cases, the aim of examination is to detect the presence or absence steroid hormone receptors (oestrogen, progesterone) in a neoplasm and to determine the percentage of tumour's cells with the presence of such receptors (so-called hormone-positive cells).
Certainly, in the application of various methods of immunohistochemical staining, a main part belongs to the Tissue Diagnostics. Thus, the positive test results for certain markers - for example, expression detection of HER2 / NEU for breast cancer or stomach (more about that will be discussed below) or the expression of c-kit in stromal tumors of the gastrointestinal tract can assign an effective therapy, or on the contrary, reject obviously useless treatment method. Using of the immunohistochemical study can also determine the degree of tumour's malignancy, and it has great practical importance in the selection of treatment.
Besides, the immunohistochemical study is successfully used in a wide range of diseases with non-tumoral nature, using various methods of staining. For example:
Direct Immunofluorescence (DIF) is used to detect a variety of autoimmune diseases, such as ordinary pemphigus (Pemphigus Vulgaris) and Bullous Pemphigoid, and renal pathologies, such as Primary IgA nephropathy (IgAN or Berger's disease), and membranous glomerulonephritis (diffuse membranous glomerulopathy). PIF is performed on frozen tissue sections.
In situ hybridization method is used for the detection of viruses, such as cytomegalovirus (CMV) and Epstein-Barr virus (EBV). Hybridization in situ is performed on paraffin slices.
IHC and HER2 status of breast cancer
There are 4 methods for determining the HER2 status of breast cancer: immunohistochemistry, SPoT-Light HER2 CISH (in situ chromogenic hybridization), Inform HER2 Dual ISH (ISH - hybridization in situ) and FISH (fluorescent hybridization in situ). Studies are performed on biopsies or surgical specimens.
As already mentioned, IHC determines the number of HER2 protein in tumour cells by staining. The expression is evaluated visually on a scale from 0 to 3+. There are 4 gradations:
0: HER2 negative breast cancer
+ or 1+: HER2 negative breast cancer. At the same time, the second test using any of these methods may be required.
++ or 2: borderline result. Obligatory re-examination by other above mentioned test.
+++ or 3++: HER2 positive breast cancer.
According to statistics, 75% of Breast Cancer have HER2 negative status, 25% - HER2 positive. In the second case, we are talking about more aggressive malignancy, however, HER2 blocking with such drugs as Herceptin (humanised monoclonal antibodies directed against the HER-2/neu) or Tykerb (another brand of the drug) can slow or even stop the growth of tumours and significantly improve the prognosis. At the same time, the mentioned drugs are toxic to the heart, so they are administered only when HER2 positive breast cancer status is confirmed. It is necessary to take into account the fact that positive status may be eventually transformed into a negative.