The HER2/neu is an oncogene that produces a protein that constitutes a receptor on the cell membrane, which in turn binds to substances that promote cell growth (growth factor). When the HER2 gene is altered, the protein that it produces can be found in larger quantities than normal, which leads to increased expression of the same and greater degree of proliferation and division of the cell. This produces an increasingly aggressive breast cancer that becomes resistant to chemotherapy and hormone therapy.

Between 25 and 30% of women with breast cancer that has been spread present an alteration of the HER2 gene. This alteration is associated with poor prognosis (higher rate of recurrence and mortality) and multiple studies have demonstrated their predictive value for sensitivity or resistance to various regimes of systemic therapy. The primary focus of this gene lies in its role as a therapeutic target of trastuzumab ( Herceptin ®), a humanized monoclonal antibody capable of blocking the action of the HER2 receptor. This new therapy was approved by the FDA in 1998, initially limiting it to patients with metastatic disease. More recently it has been shown that the use of trastuzumab in the initial stages of the disease, as a single agent or in combination regimens, significantly reduces the risk of recurrence and mortality.

The “In Situ” hybridization Fluorescent (FISH) is one of the methods used for the study of HER2/neu, which assesses the number of copies of the gene in the cell nucleus to detect its amplification. The test is used at the Punta Pacifica Center for Genetics, called PATHVYSION has been approved by the United States Food and Drug Administration.

When is FISH needed for an immunohistochemical breast cancer?
If the immunohistochemistry (herceptest) is positive (3 +), the patient is eligible to be treated with Herceptin ®. When an inmunohistochemical gives an erroneous result (2 +), it is necessary to verify that the HER2 gene has amplified. The most common way to check this amplification is with Fluorescence In Situ Hybridization (FISH).

Moreover, today, many of these genetic tests are essential to identify and assess the therapeutic efficacy of drugs specifically targeted toward the genetic defect that causes neoplasia.

This innovative diagnostic methodology was standardized and validated by Dr. Sergio Sanchez, director of the Laboratory of Surgical Pathology and Cytology, University Hospital of Puebla, Mexico.