title: The combination of letrozole and trastuzumab as first or second-line biological therapy produces durable responses in a subset of HER2 positive and ER positive advanced breast cancers.
abstract: BACKGROUND
  Estrogen receptor (ER) and/or progesterone receptor expression occurs in approximately 50% HER2 positive (HER2+) breast cancers and cross-talk between the estrogen and HER2 pathways promotes endocrine therapy resistance. The efficacy of the aromatase inhibitor letrozole in combination with trastuzumab was therefore tested in a Phase 2 study.
  
  
  METHODS
  Patients with ER+ and/or PgR+ and HER2+ (IHC 2+ or 3+ or FISH+) advanced breast cancer were treated with trastuzumab plus letrozole until disease progression or unacceptable toxicity.
  
  
  RESULTS
  Thirty-three patients were enrolled, of which thirty one were considered evaluable. The majority of patients (82%) had received tamoxifen and 82% had HER2 FISH+ and/or IHC 3+ tumors. Eight patients responded (1 CR and 7 PR) for an overall response rate (ORR) of 26% and a clinical benefit rate (CBR) of 52%. The median time to progression (TTP) was 5.8 months and the median duration of response (DOR) was 20.6+ months. Excluding IHC 2+, FISH- tumors, the OR was 24%, CBR 44%, TTP 5.5 months and DOR 17+ months. The combination was well tolerated with only two toxicity events requiring termination of study medication.
  
  
  CONCLUSIONS
  Combined trastuzumab and letrozole treatment for patients with HER2+ and ER+ advanced breast cancer produced durable responses consistently lasting at least 1 year in one quarter of the patients. While these data are promising for a subgroup, for half the patients, trastuzumab plus letrozole was inactive. This finding demonstrates ER+ HER2+ advanced disease is heterogeneous and additional agents will be required for optimal management based on targeted therapeutics alone.
authors.affiliation: Siteman Comprehensive Cancer Center, Washington University School of Medicine, 660 South Euclid Ave, Campus Box 8056, St Louis, MO, USA
authors.forename: P Kelly
authors.initials: PK
authors.lastname: Marcom
authors.forename: Claudine
authors.initials: C
authors.lastname: Isaacs
authors.forename: Lyndsay
authors.initials: L
authors.lastname: Harris
authors.forename: Zee Wang
authors.initials: ZW
authors.lastname: Wong
authors.forename: Aruna
authors.initials: A
authors.lastname: Kommarreddy
authors.forename: Nellie
authors.initials: N
authors.lastname: Novielli
authors.forename: Gretchen
authors.initials: G
authors.lastname: Mann
authors.forename: Yu
authors.initials: Y
authors.lastname: Tao
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Ellis
mesh_terms: D000328:Adult; D000368:Aged; D000911:Antibodies, Monoclonal / Q000008:administration & dosage* / Q000009:adverse effects; D061067:Antibodies, Monoclonal, Humanized; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000737:chemistry / Q000188:drug therapy*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D017404:In Situ Hybridization, Fluorescence; D000077289:Letrozole; D008875:Middle Aged; D009570:Nitriles / Q000008:administration & dosage* / Q000009:adverse effects; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000032:analysis*; D011960:Receptors, Estrogen / Q000032:analysis*; D000068878:Trastuzumab; D014230:Triazoles / Q000008:administration & dosage* / Q000009:adverse effects
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000077289:Letrozole; D009570:Nitriles; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D000068878:Trastuzumab; D014230:Triazoles