title: Trastuzumab and antiestrogen therapy: focus on mechanisms of action and resistance.
abstract: OBJECTIVE
  In breast cancer, 2 molecular targets are well established (ER/PR and HER2), and therapies directed to these proteins have demonstrated to be clinically useful.
  
  
  METHODS
  Despite the presence of the ER and PR, only half of the patients will respond to endocrine therapy, and less than 35% of patients with ErbB2-overexpressing metastatic breast cancer will respond to trastuzumab as a single agent.
  
  
  RESULTS
  To improve survival of metastatic breast cancer patients with ER/PR positive and HER2 positive is critical to elucidate the mechanism of resistance or sensitivity of these tumors for a better selection depending on biologic molecular alterations.
  
  
  CONCLUSIONS
  Recently, several studies addressing this issue have been reported. Here, we will focus on a comprehensive review of the currently available data.
authors.affiliation: Servicio de Oncología Médica, Hospital Universitario de Salamanca, Salamanca, Spain. aocana@vhebron.net
authors.forename: Alberto
authors.initials: A
authors.lastname: Ocaña
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Cruz
authors.forename: Atanasio
authors.initials: A
authors.lastname: Pandiella
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology* / Q000627:therapeutic use; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy*; D019008:Drug Resistance, Neoplasm; D020847:Estrogen Receptor Modulators / Q000494:pharmacology* / Q000627:therapeutic use; D005260:Female; D006801:Humans; D011379:Prognosis; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis / Q000096:biosynthesis*; D011960:Receptors, Estrogen / Q000032:analysis; D011980:Receptors, Progesterone / Q000032:analysis; D016019:Survival Analysis; D000068878:Trastuzumab; D016896:Treatment Outcome
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D020847:Estrogen Receptor Modulators; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D000068878:Trastuzumab