HER2 is a transmembrane growth factor receptor found in normal and malignant breast epithelial cells. Phosphorylation of the intracellular tyrosine kinase results in intracellular signaling and activation of genes involved in cell growth. Overexpression of HER2 has independent prognostic significance in early breast cancer and may also predict response to hormonal and cytotoxic therapies, although this latter role is less well studied. Prospective stratification of HER2 status in current clinical trials may more accurately delineate these roles. Anti-HER2 therapy, using a humanized monoclonal antibody, has enhanced survival when given with chemotherapy compared with chemotherapy alone in patients with metastatic HER2-overexpressing breast cancer. A potential limitation to its use in the adjuvant setting is the increased incidence of cardiotoxicity in patients treated either concurrently or previously with anthracyclines; carefully designed prospective adjuvant trials are currently being launched. HER2 is a relatively new prognostic marker and holds promise for predicting response to various therapies and for target-specific therapy.
Copyright 2001 by W.B. Saunders Company.