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

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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 963 (94%) treated HER2+ patients with recorded HR tumor status, 55% (533) were HR+ and 45% (430) were HR-negative. 1st-line MBC treatment regimens for HER2+/HR+ patients included endocrine therapy (E) only, 57 (10.7%); E + trastuzumab (T), 50 (9.4%); chemotherapy (C) ± E, 41 (7.7%); and C + trastuzumab (T) ± E, 361 (67.7%). Progression-free survival (PFS) and overall survival (OS) by 1st line treatment groups are in the table. Conclusions: In registHER, HER2+/HR+ patients treated with E+T had longer PFS than patients treated with E alone; E- alone median PFS is consistent with findings in prospective randomized trials. These data provide further information regarding trastuzumab's role in targeting dual pathways in HER2+/HR+ MBC patients in a real-world setting. Multivariate analysis to address potential bias from known prognostic factors that may influence treatment choice will be presented.

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