title: Cytoplasmic estrogen receptor in breast cancer.
abstract: OBJECTIVE
  In addition to genomic signaling, it is accepted that estrogen receptor-α (ERα) has nonnuclear signaling functions, which correlate with tamoxifen resistance in preclinical models. However, evidence for cytoplasmic ER localization in human breast tumors is less established. We sought to determine the presence and implications of nonnuclear ER in clinical specimens.
  
  
  METHODS
  A panel of ERα-specific antibodies (SP1, MC20, F10, 60c, and 1D5) was validated by Western blot and quantitative immunofluorescent (QIF) analysis of cell lines and patient controls. Then eight retrospective cohorts collected on tissue microarrays were assessed for cytoplasmic ER. Four cohorts were from Yale (YTMA 49, 107, 130, and 128) and four others (NCI YTMA 99, South Swedish Breast Cancer Group SBII, NSABP B14, and a Vietnamese Cohort) from other sites around the world.
  
  
  RESULTS
  Four of the antibodies specifically recognized ER by Western and QIF analysis, showed linear increases in amounts of ER in cell line series with progressively increasing ER, and the antibodies were reproducible on YTMA 49 with Pearson correlations (r(2) values) ranging from 0.87 to 0.94. One antibody with striking cytoplasmic staining (MC20) failed validation. We found evidence for specific cytoplasmic staining with the other four antibodies across eight cohorts. The average incidence was 1.5%, ranging from 0 to 3.2%.
  
  
  CONCLUSIONS
  Our data show ERα is present in the cytoplasm in a number of cases using multiple antibodies while reinforcing the importance of antibody validation. In nearly 3,200 cases, cytoplasmic ER is present at very low incidence, suggesting its measurement is unlikely to be of routine clinical value.
authors: Department of Pathology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
authors: Allison W
authors: AW
authors: Welsh
authors: Donald R
authors: DR
authors: Lannin
authors: Gregory S
authors: GS
authors: Young
authors: Mark E
authors: ME
authors: Sherman
authors: Jonine D
authors: JD
authors: Figueroa
authors: N Lynn
authors: NL
authors: Henry
authors: Lisa
authors: L
authors: Ryden
authors: Chungyeul
authors: C
authors: Kim
authors: Richard R
authors: RR
authors: Love
authors: Rachel
authors: R
authors: Schiff
authors: David L
authors: DL
authors: Rimm
mesh_terms: D000911:Antibodies, Monoclonal; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology*; D003593:Cytoplasm / Q000378:metabolism*; D047628:Estrogen Receptor alpha / Q000276:immunology / Q000378:metabolism*; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D007124:Immunoenzyme Techniques; D015337:Multicenter Studies as Topic; D012189:Retrospective Studies; D046888:Tissue Array Analysis; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha