Prognostic and predictive implications of HER2 status for breast cancer patients

Women diagnosed with breast cancer face many emotional and psychological challenges, which are often related to how they perceive their chances of survival. A number of factors are known to be indicators of breast cancer prognosis, including tumour type, size and grade, and lymph node status. These factors can be used alone or in combination to make management decisions based on a broad assessment of tumour aggression. However, identifying an independent marker of prognosis has proved more difficult. The human epidermal growth factor receptor-2 (HER2) is amplified/overexpressed in 25-30% of breast tumours. This event has been shown to be associated with poor prognosis in breast cancer patients. Initial observations indicated that median survival duration is reduced by at least 50% in patients who overexpress HER2 compared with those who do not overexpress the receptor. This finding has been supported by many subsequent studies and data are accumulating to indicate that the relationship holds for both node-negative and node-positive patients. This could be particularly important for identifying the 30% of node-negative patients who will progress despite therapy. HER2 status may also be able to predict the outcome of therapy. It appears likely that HER2 overexpression predicts for resistance to tamoxifen and other hormonal therapies. It is also possible that HER2-overexpressing patients may respond better to dose-intense anthracycline therapy and worse to cyclophosphamide/methotrexate/5-fluorouracil than non-overexpressing patients. Explaining these associations to patients may empower them to deal with the psychological effects of a diagnosis of breast cancer while providing hope for the future.