Her-2/neu testing is primarily used to select patients for treatment with Herceptin (trastuzumab). It may also be used to help determine how aggressive a breast cancer tumour is likely to be.

It is also used as a predictor of response to certain types of chemotherapy and hormone therapy but these findings require further validation.

The serum Her2/neu test is sometimes used to monitor cancer therapy. If the level is initially elevated then falls, it is likely that treatment is working; if it stays elevated, treatment is not working; and if the level falls then rises, the cancer may be recurring.

Her-2/neu testing is recommended as part of an initial workup of invasive breast cancer and is sometimes done with recurrent breast cancer. It is not diagnostic but helps the doctor determine treatment options and understand more about the tumour’s characteristics.

Serum Her-2/neu is sometimes requested initially to establish a baseline and then, if elevated, used to monitor cancer treatment.

A positive tissue (IHC) Her-2/neu test means that the Her-2/neu gene is over-expressing (producing an excess amount of) Her-2/neu protein. If a FISH test is done, then amplification (production of too many copies) of the Her-2/Mneu gene can be detected. If either test is positive, the patient is likely to have an aggressive tumour. HER-2 positive patients are potential candidates for Herceptin therapy. [See "Is there anything else I should know?"].

Currently, Herceptin is approved in Australia for the treatment of Her-2 positive early stage breast cancer and Her-2 positive advanced breast cancer.

If the IHC test is negative but the FISH test is positive, the patient still may benefit from Herceptin, but if both are negative the treatment will not be useful.

Her-2/neu-positive tumours may be susceptible to Herceptin (trastuzumab), a therapy created to target Her-2/neu protein. Herceptin, an antibody made in the laboratory, attaches itself to the excess protein molecules and inhibits the growth of the cancer. The development of this specialized therapy has increased the use of Her-2/neu testing. Herceptin may be used alone or with some chemotherapy agents but is only useful in those who have Her-2/neu amplification and protein over-expression.

Tissue Her-2/neu testing is not available in every laboratory. Both IHC and FISH require experience and special training to perform and interpret.