Independent characterization by duel staining of progesterone receptor (PR) and estrogen receptor (ER) in breast cancer (BC).

596 Background: The oncology literature indicates that ER and PR are linked and in BC the presence of PR usually indicates functional ER. BCs express both ER and PR to varying degree, but little has been published on expression of ER + PR in individual cancer cells. The goal of this study is to 1. Determine the expression ER and PR at the cellular level, 2. Determine if ER and PR are expressed in the same BC cells. If ER and PR are separate, this may indicate that antiestrogens and antiprogestins may target different cells. Methods: Archived 1° BC specimens were processed using standard IHC techniques for ER/PR testing. The procedure consisted of sequential double staining on the same microtone section, where the PR was visualized through brown staining using HRP/DAB, and the ER was visualized through red staining using AP/Permanent Red. The initial testing on 13 tumor samples utilized a duel anti-PR-A/B antibody (Ab) and an ER Ab. The next 63 tumor samples utilized; 1. anti-ER and anti-PR-A Abs, 2. anti-...