The effect of trastuzumab therapy on clinical benefit from fulvestrant treatment for metastatic estrogen receptor-positive breast cancer patients.

155 Background: Overexpression of HER2/neu is associated with tamoxifen resistance in breast cancer (Osborne CK et al. J Natl Canc Inst 2003; 95:353-361). However pts may present with both estrogen receptor (ER) and HER2/neu + tumors. The benefit of adding fulvestrant to trastuzumab is unclear. The objective of the study was to determine the effect of trastuzumab on fulvestrant therapy. Methods: This was an IRB approved record review of patients (pts) from three medical oncologists with biopsy-proven ER+ metastatic breast cancer treated with fulvestrant who also had their primary tumor tested for HER2/neu. Demographic data collected included age at diagnosis, type and stage of cancer, original and metastatic ER, progesterone receptor (PR), and HER-2/neu biomarkers, and site(s) of metastasis, and primary local and systemic treatment. All pts with HER-2/neu + primary tumors received trastuzumab. The duration of fulvestrant therapy was calculated. Time to clinical disease progression on fulvestrant was measu...