title: The role of HER-2 oncoprotein in drug-sensitivity in breast cancer (review).
abstract: Overexpression of human epidermal growth factor receptor-2 (HER-2) oncoprotein is an important prognostic factor associated with a poor prognosis in breast cancer. Although treatment with trastuzumab, an anti-HER-2 antibody, increases drug-sensitivity in vitro and in vivo, the role of HER-2 oncoprotein in drug-sensitivity is still uncertain. The present work discusses the clinical significance of the HER-2 oncoprotein in drug-sensitivity in breast cancer based on previous clinical and basic results and reviews the current concept of HER-2 oncoprotein in drug-sensitivity. Introduction of HER-2 oncoprotein in vitro induces resistance to several anticancer drugs, including taxanes, cisplatin (CDDP) and 5-fluorouracil (5-FU) in breast cancer cells. The acquisition of drug-resistance by introduction of the HER-2 gene, however, depends on the cell type, because transfection of the HER-2 gene per se does not necessarily induce resistance to the same drugs in all types of breast cancer cells. In clinical studies, patients with HER-2 overexpression responded better to an anthracycline-based regimen than patients with low HER-2 expression, and their overall survival was also superior. In contrast, a correlation between the response to a cyclophosphamide + methotrexate + 5-FU regimen and overexpression of HER-2 is not certain. Taxanes responsiveness in patients with HER-2 oncoprotein overexpression was superior in patients with low HER-2 expression. Treatment with trastuzumab increased drug-sensitivity to anthracyclines, CDDP, and taxanes, but not to 5-FU, in breast cancer cells. Although the mechanism(s) by which trastuzumab enhances drug-sensitivity is not fully understood, modulation of the signal transduction pathways leading to apoptosis, such as down-regulation of the anti-apoptotic protein, Bcl-2, might be an important target to increase drug-sensitivity in breast cancer. HER-2 overexpression can be a good indicator for the selection of aniticancer drugs, especially for anthracycline containing regimens. To modulate HER-2-targeting therapy, the mechanism(s) by which trastuzumab enhances drug-sensitivity requires elucidation at the molecular level, including determination of other factors that influence drug-sensitivity, leading to a more promising treatment for individual patients receiving combination therapy with trastuzumab and anticancer drugs for breast cancer.
authors.affiliation: Department of Surgical Oncology, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima 734-8553, Japan. rkim@pc.hiroshima-u.ac.jp
authors.forename: Ryungsa
authors.initials: R
authors.lastname: Kim
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Tanabe
authors.forename: Yoko
authors.initials: Y
authors.lastname: Uchida
authors.forename: Akihiko
authors.initials: A
authors.lastname: Osaki
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Toge
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000175:diagnosis / Q000188:drug therapy* / Q000378:metabolism; D017024:Chemotherapy, Adjuvant; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D008198:Lymph Nodes / Q000473:pathology; D008207:Lymphatic Metastasis; D011379:Prognosis; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000502:physiology*
chemical_list: D000970:Antineoplastic Agents; D018719:Erb-b2 Receptor Tyrosine Kinases