HER-2 testing

HER-2 testing is primarily used to select patients for treatment with HER-2 targeted therapy such as trastuzumab (Herceptin). Other HER-2 targeted therapies have also been licenced. These agents are used in the UK to treat patients with HER-2 positive early stage breast cancer, either prior to surgery and chemotherapy, or sometimes afterwards. It reduces the risk of the cancer coming back and increases the chances of cure.

Herceptin is also used for patients with advanced breast cancer that has spread elsewhere within the body or recurred after initial treatment.

HER-2 testing may also be used to help determine how aggressive a cancer is likely to be. It is also used to predict the response to certain types of chemotherapy and hormone therapy.

HER-2 testing is recommended as part of an initial workup of invasive breast cancer. It is sometimes done with recurrent or metastatic breast cancer, or in some other cancers. It helps the doctor determine treatment options and understand more about the cancer’s characteristics.

A positive HER-2 IHC test means that there is an excess amount of HER-2 protein on the surface of the cancer cells (the HER-2 gene product is overexpressed). A positive FISH test indicates there is HER-2 gene amplification in the cancer cell nucleus meaning it is producing too many copies of the HER-2 gene. If either test is positive, the patient is likely to have a more aggressive tumour. If the cancer is HER-2 positive, the patient may be treated with trastuzumab (Herceptin) or other HER-2 targeted therapy. [See "Is there anything else I should know?"].

HER-2-positive tumours may be susceptible to trastuzumab (Herceptin), and other drug therapies created to target HER-2 protein. These drugs attach to the cancer cell surface and inhibit the growth of the cancer. The development of specialised therapies has increased the importance of HER-2 testing. Herceptin and other HER-2 targeted therapy may be used alone or with other chemotherapy agents. They are only useful in those who have a HER-2 positive cancer.

HER-2 testing is not available in every pathology laboratory. IHC, FISH and CISH require experience and special training to perform and interpret. Your doctor may need to send your sample to a reference laboratory and the results may take over a week to return.

During the initial workup of invasive breast cancer, your doctor will also test for hormone receptor status. Cancers with a positive oestrogen and/or progesterone receptor status may not respond as well to endocrine or hormone therapy if they are also HER-2-positive.