Impact of HER2-targeted therapy on overall survival (OS) in patients (pts) with HER2-positive (HER2+) metastatic breast cancer (MBC).

572 Background: Trastuzumab (T) prolongs OS over chemotherapy alone in pts with HER2+ MBC. Upon disease progression, pts may switch to lapatinib (L) or continue on T. We aimed at assessing the impact of both strategies on OS in all pts treated for HER2+ MBC at the Department of Medicine 1, Medical University of Vienna, from 1999-2009. Methods: 201 pts were identified from a BC databank. 115 pts (572%) received multiple lines of T, whereas 58 (28.9%) were treated with a single line of T-based palliative therapy. A control group of 28 pts (13.9%) had never received T as they were treated before 1999, when T was introduced. HER2 was determined by immunohistochemistry and reanalyzed by FISH if a score of 2+ was gained. OS from diagnosis of metastatic disease was defined as primary study endpoint and estimated using the Kaplan-Meier method. A Cox proportional hazards model was applied to correct for other factors associated with OS. Results: T significantly prolonged OS in HER2+ MBC (41 vs. 13 months; p<0.001)...