The value of the human epidermal growth factor receptor-2 (HER2) as a prognostic marker

The prognosis for patients with breast cancer is determined by well-establi shed pathological features associated with biological aggressiveness, histo logical grade, tumour size and nodal involvement. These remain the key dete rminants, despite the identification of numerous other potential biological markers. The use of prognostic indices, such as the Nottingham Prognostic Index (NPI), which combines and weights these factors: enables clinicians t o predict outcome with a certain amount of accuracy. Approximately 20-30% o f breast cancers express very high quantities of the human epidermal growth factor receptor-2 (HER2) protein and this is almost always associated with gene amplification. With the use of sensitive techniques, such as the radi o-immunohistochemical method (rIHC) described herein, to quantify HER2 prot ein levels, up to a further 50% of such cancers will be found to express th e HER2 receptor at least 4-fold higher than normal breast cells. Adding HER 2 expression to the NPI helps to determine more accurately the prognosis fo r individual patients, particularly those with node-negative disease. Overa ll, the main value of HER2 measurement is likely to be in the prediction of response to therapies targeting the HER1 gene and protein. (C) 2001 Elsevi er Science Ltd. All rights reserved.