title: Association of Over-Expressed Estrogen Receptor Alpha with Development of Tamoxifen Resistant Hyperplasia and Adenocarcinomas in Genetically Engineered Mice.
abstract: BACKGROUND
  Estrogen receptor alpha (ERα) and cyclin D1 are frequently co-expressed in human breast cancer. Some, but not all, studies link tamoxifen resistance to co-expression of cyclin D1 and ERα. In mice over-expression of either cyclin D1 or ERα in mammary epithelial cells is sufficient to induce mammary hyperplasia. Cyclin D1 over-expression in mice leads to mammary adenocarcinoma associated with activated estrogen signaling pathways. ERα over-expression in mice leads to mammary hyperplasia and cancer. Significantly, disease development in these mice is abrogated by loss of cyclin D1.
  
  
  METHODS
  Genetically engineered mouse models were used to determine whether or not ERα over-expression demonstrated cooperativity with cyclin D1 over-expression in cancer development, reaction to the chemical carcinogen DMBA, or tamoxifen response.
  
  
  RESULTS
  Adding ERα over-expression to cyclin D1 over-expression increased the prevalence of hyperplasia but not cancer. Single dose DMBA exposure did not increase cancer prevalence in any of the genotypes although cyclin D1 over-expressing mice demonstrated a significant increase in hyperplasia. Tamoxifen treatment was initiated at both young and older ages to test for genotype-specific differences in response. Although normal ductal structures regressed in all genotypes at both younger and older ages, tamoxifen did not significantly reduce the prevalence of either hyperplasia or cancer in any of the genotypes. All of the cancers that developed were hormone receptor positive, including those that developed on tamoxifen, and all showed expression of nuclear-localized cyclin D1. In summary, development of tamoxifen resistant hyperplasia and cancer was associated with expression of ERα and cyclin D1.
  
  
  CONCLUSIONS
  These preclinical models will be useful to test strategies for overcoming tamoxifen resistance, perhaps by simultaneously targeting cell cycle regulatory pathways associated with cyclin D1.
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, 20007, USA.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Miermont
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, 20007, USA.
authors.forename: Marina Carla
authors.initials: MC
authors.lastname: Cabrera
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, 20007, USA.
authors.forename: Silvina M
authors.initials: SM
authors.lastname: Frech
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, 20007, USA.
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Nakles
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, 20007, USA.
authors.forename: Edgar S
authors.initials: ES
authors.lastname: Diaz-Cruz
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, 20007, USA ; Department of Biology, Georgetown University, Washington, DC, 20007, USA.
authors.forename: Maddalena Tilli
authors.initials: MT
authors.lastname: Shiffert
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, 20007, USA ; Department of Medicine, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, 20007, USA ; Department of Nanobiomedical Science and WCU Research Center of Nanobiomedical Science, Dankook University, Chungnam 330-714, Korea.
authors.forename: Priscilla A
authors.initials: PA
authors.lastname: Furth
keywords: Breast cancer; Cyclin D1; ERα; Hyperplasia, Tamoxifen; Mouse models