registHER: Treatment outcomes in patients with HER2-positive (HER2+), hormone receptor-positive (HR+) metastatic breast cancer (MBC)

1057 Background: Approximately 50% of HER2+ breast cancers are HR+ (defined as estrogen receptor [ER] and/or progesterone receptor[PR] positive). Cross talk between growth factor and ER-dependent signaling pathways may affect growth regulation in HER2+ breast cancers. Blockade of both pathways appears to be more active than blocking either alone based on randomized trials performed in selected populations. However, the outcomes of HER2+ and HR+ MBC patients relative to those in real- life clinical practice have not been evaluated in large cohort studies. Methods: registHER is a prospective observational study of 1023 patients with newly diagnosed (within 6 months [mo]) HER2+ MBC treated in community/academic settings, enrolled from 12/03 to 2/06. Median follow-up from MBC diagnosis was 25 mo at data cutoff (1/02/08). Treatment patterns and outcomes in patients with HER2+/HR+ MBC receiving 1st-line therapy (i.e., therapies received prior to 1st progression) are described in this analysis. Results: Of the ...