FISH - HER -2 / NEU ONCOGENE AMPLIFICATION

FISH test for HER-2/NEU ONCOGENE AMPLIFICATION TEST

WHAT IS HER2/NEU?

Her2 stands for Human epidermal growth factor receptor-2 and is a gene involved in normal cell growth. This gene is expressed on the surface of all breast cells. Amplification of the Her2/neu gene in some cancers enables it to spread faster and grow more rapidly. However, such tumours are candidates for Her2/neu targeted therapy. Amplification of this gene is seen in about 20% of all breast carcinoma, as well as in some other tumours such as gastric and esophageal carcinomas. Her2/neu amplification is also assessed in metastatic tumour sites, as even these patients benefit from targeted therapy.

Currently, clinical trials are underway to study the possible role of Her2/neu amplification in the pathogenesis of many non-breast /gastro-intestinal tumours as well. This would help to benefit patients of other cancers as well by improving response using targeted therapy.

WHAT IS A FISH TEST?

FISH stands for fluorescence in-situ hybridization and is used to identify particular genes of interest in cells using fluorescent markers. This test can be used to identify over-expression of the Her2/neu gene in tumour cells.

WHEN IS FISH TEST FOR HER2/NEU AMPLIFICATION PRESCRIBED FOR BREAST TUMOURS?

It is essential to know the Her2/neu amplification status in tumours to ensure that the best possible treatment is provided. It also helps in the assessing the prognosis of the patient and estimating the risk of recurrence.

Amplification of Her2/neu gene causes over-expression of the protein Her2/neu which can be identified by a test known as immunohistochemistry (IHC) done on the tumour tissue. A positive score (score 3+) on IHC confirms the presence of Her2/neu amplification and the patients are taken up for targeted therapy. Tumours which show equivocal results on immunohistochemistry with Her2/neu (score 2+), are usually taken up for FISH studies for Her2/neu amplification. FISH test is therefore a reflex test that is performed on the request of the clinician when there is an equivocal result on immunohistochemistry.

It is essential to determine accurately the presence or absence of Her2/neu amplification using the correct test methods and reading of results by trained Pathologists. A wrong positive result may lead to unnecessary adverse effects of targeted therapy, as the drugs are cardiotoxic. An inaccurate negative result may lead to less than optimum treatment for the patient.

WHAT IS REQUIRED FOR A FISH TEST FOR HER2/NEU GENE AMPLIFICATION?

A FISH test is performed on a paraffin sections obtained from a tissue biopsy. This tissue may be a core biopsy or an excision biopsy specimen. After a satisfactory clinical examination, the procedure is explained to the patient and is performed by the treating surgeon. The biopsy is then processed for histopathological examination followed by immunohistochemistry.

Immunohistochemical studies are done on the tumour tissue. An equivocal score (or positive score in some cases) on immunohistochemistry prompts a reflex FISH test to be done.

UNDERSTANDING THE RESULTS OF YOUR FISH TEST FOR HER2/NEU AMPLIFICATION.

The FISH test for Her2/neu gene amplification is given as positive or negative for Her2/neu gene amplification. These results are considered along with the histopathological report, the results of the immunohistochemical tests as well as radiological findings to decide the treatment plan and also the prognosis of the cancer.