ne or paracrine stimulation of these receptors. The best characterized are those that constitute the ErbB family of tyrosine kinase receptors (also known as tyrosine kinase type I receptors). This family is made up of four members: the receptor for epidermal growth factor (EGFR, ErbB-1 or HER1) and their homologues HER2 (ErbB-2), HER3 (ErbB-3) and HER4 or ErbB-4 1,2 . These receptors, located in the plasmic membrane, are made up of an extracelular domain for binding by means of li- 172 REVISIONES Trastuzumab (Herceptin) in the treatment of breast cancer with HER2 overexpression Joel M. Salazar Cavazos a, b , Juan Francisco González Guerrero a , William O. Brito Villanueva a , Joan Albanell Mestres b and José M. Baselga Torres b a Centro Universitario Contra el Cáncer. UANL Monterrey, Nuevo León. México. b Servicio de Oncología Médica. Hospital Universitario Vall d’Hebron. Barcelona. HER2 is a 185 kDa transmembrane recep- tor with tyrosine kinase activity encoded by the HER2/neu gene. HER2 is overex- pressed in 25%-30% of breast cancer and confers an agressive clinic course. Tras- tuzumab (Herceptin) is a monoclonal anti- body directed against HER2 receptor that has a favorable toxicity profile and pro- duces responses as a single agent in wo- men with metastatic breast cancer with HER2 overexpression. A multicenter pha- se IIItrial in HER2 positive metastatic breast cancer, compared first line che- motherapy with adriamycin/cyclophosp- hamide or paclitaxel alone or the same chemotherapy plus trastuzumab. Response rate, duration of response and time to progression, were better with the combi- nation. Remarkably, overall survival was significantly improved in patients with trastuzumab and chemotherapy. These studies led to the approval of trastuzu- mab for HER2 positive metastatic breast cancer. Ongoing trials are analyzing new combinations of trastuzumab and chemot- herapy or hormonal therapy. The role of trastuzumab in adjuvant and neoadjuvant therapy is also under investigation. Key words: Breast cancer, trastuzumab, hercep- tin, HER2. Rev Oncología 2001; 4: 172-182. INTRODUCTION Some cancers express high levels of growth fac- tors as well as of their receptors. The growth of cells of breast cancer is regulated by the autocri- Correspondence: Dr. J. M. Salazar Cavazos. Centro Universitario Contra el Cáncer. Ave. Madero y Gonzalitos. 64020 Monterrey, Nuevo León (México). Recibido el 2-1-2001. Aceptado para su publicación el 7-5-2001.