Outcomes Of Single Versus Double Hormone Receptor Positive Breast Cancer.

569Background: Retrospective data suggest that compared to double hormone receptor positive (HR+) (estrogen [ER+] and progesterone receptor [PgR+] positive), single receptor-positive (ER+/PgR- or ER-/PgR+) breast cancer (BC) patients have worse outcomes. Additionally, whether the ER-/PgR+ group is a real phenomenon or an analytic artifact remains elusive. Here, we evaluate the molecular classification and clinical outcomes of single versus double receptor positive BC patients enrolled in the GEICAM/9906 trial. Methods: We analyzed data from the GEICAM/9906 trial, a prospective adjuvant randomized phase-III study comparing six cycles of FEC to four cycles of FEC followed by eight weekly cycles of paclitaxel. HR+ patients received endocrine treatment at completion of chemotherapy. HER2+ patients did not receive adjuvant trastuzumab. Archival tumors were retrieved retrospectively and classified into intrinsic subtypes using the PAM50 gene expression assay. Distant metastasis free survival (DMFS) and overall ...