The HER2 receptor, or human epidermal growth factor receptor 2, is a gene that can affect the development of breast cancer. When the patient undergoes a pathological examination, the latter must include information on the status of the HER2 receptor, since this data tells us whether the gene in question affects the formation of the tumor.
Genes contain the formulas of different proteins that a cell needs to stay healthy. Some genes, as well as the proteins they produce, can affect the onset and development of breast cancer.
Therefore, we analyze the cancerous cells from a tissue sample by biopsy, or other techniques in order to see which genes are found in normal conditions and which, instead, are altered. It is also possible to analyze the proteins produced by the cells.
Background information on breast cancer
Breast cancer forms in breast cells. It can develop in both men and women. Nonetheless, cases of breast cancer in men account for only 1% of total cases.
In Italy, one in eight women is affected by breast cancer: it is in fact the cancer that has the highest incidence among women. In addition, it accounts for 30% of all cancer diagnoses. The incidence has increased following the introduction of mammography in screening programs and continues to increase due to an aging population.
This tumor develops as a result of the uncontrolled reproduction of some cells of the mammary glands. The tumor can appear in different structures of this organ, such as the ducts. As it proliferates, some proteins and molecules become more numerous, as in the case of the HER2 receptor or the proliferation marker Ki67.
Certain risk factors considerably increase the chances of suffering from this disease. Among them, we can mention the following:
- Genetic predisposition.
- History of atypical hyperplasia.
- Not having children or having them in old age.
- Exposure to estrogen.
- Sedentary lifestyle.
- Nutrition: the Mediterranean diet reduces the risk of suffering from breast cancer by 30%; however, the Western diet increases it.
HER2 proteins are breast cell receptors produced by the HER2 gene. Under normal conditions, these receptors are needed for healthy breast growth and for breast cells to divide and repair themselves.
In 25% of breast cancers, however, the gene that encodes the HER2 receptor proteins does not function properly and produces a high number of copies of itself. This phenomenon is known as amplification of the HER2 gene.
All extra copies of this gene send the instruction to synthesize other HER2 receptors, creating overexpression. As a result, breast cells grow and divide uncontrollably, causing the tumor to form.
Breast cancer HER2 + or HER2 –
Based on the presence or absence of amplification of this gene, breast cancer can be classified into:
- HER2 positive : Breast cancer showing amplification of the HER-2 gene or overexpression of this protein.
- HER2 negative : occurs when the tumor is not overexpressing the gene or the HER2 protein.
In general, the positive HER2 type has a negative prognosis, because it tends to grow faster, therefore to spread and form again.
However, recent advances in research have made it possible to develop new anti-HER2 drugs that have yielded excellent results. An example is represented by trastuzumab.
Determination of the HER2 receptor in breast cancer patients
Today there are 4 clinical tests that allow to detect the presence of this receptor:
- Immunohistochemistry or IHC : This analysis indicates a possible excess of HER2 protein in cancer cells. The results are expressed as follows: 0 (negative), 1 + (negative), 2 + (ambiguous), or 3 + (positive).
- FISH or fluorescent in situ hybridization analysis. The results of this test let you know if there is an excess of copies of the HER-2 gene in the affected cells.
- CISH or chromogenic hybridization in situ with subtraction probe technology : like the previous examination, it reveals a possible excess of copies of the HER2 gene.
- ISH or HER2 analysis by in situ hybridization : shows the same information obtained from previous examinations.