Immunohistochemistry Staining Validation And Prevalence Of The Estrogen Receptor Coactivator Med1 In Primary And Metastatic Hormone Receptor Positive Breast Cancer.

e11548 Background: MED1 is an estrogen receptor coactivator that is associated with resistance to antiestrogen therapy, and silencing MED1 sensitizes breast cancer cells to fulvestrant Cross talk between MED1 and HER-2 regulates tamoxifen resistance There is a need to standardize immunohistochemical (IHC) expression of MED1 in breast cancer and to determine the prevalence of overexpression in breast cancer Methods: This IRB approved study evaluated ER positive primary or metastatic breast cancers from patients treated at the University of Cincinnati Utilizing an antibody against the C-terminus of MED1, IHC was performed on paraffin embedded tissue All slides were evaluated by breast pathologist; and to establish inter-reader agreement, some specimens were read by two pathologists Nuclear staining was interpreted in a semi-quantitative modified Allred method. Proportion scores from 1 - 5 were assigned based on percentage of stained tumor cells as a continuous variable with cutpoints as follows: 0-5% (score...