ER-/PgR+ breast cancer is a separate entity characterized by distinct phenotype: Comprehensive reevaluation of cases from Polish and Hungarian centers.

e12554 Background: ER negative (-)/PgR positive (+) breast cancer (BC) is very uncommon and questioned by many experts. We comprehensively reevaluated ER-/PgR+ BCs in the large cohort from Polish and Hungarian centers. Methods: FFPE blocks from 105 ER-/PgR+ tumors (45 breast biopsies and 64 post-operative samples from tumors not exposed to systemic therapy) were collected from 10 Polish and 3 Hungarian centers. In 60 cases available original slides with ER/PgR staining underwent reevaluation by 3 pathologists (MK, RP, WB) for ER and PgR expression by ASCO/CAP criteria. Subsequently, all samples were stained with 3 antibodies against ER (Dako monoclonal (MC) mouse anti-ERα, clone 1D5; Dako …