Predicting response to second-line trastuzumab-based therapy in patients (pts) with HER2-positive advanced breast cancer (ABC)

1090 Background: In HER2-positive ABC, the upfront use of trastuzumab (T) is well established. Following progression upon first-line therapy, pts may be switched to lapatinib. Others however may be candidates for continued antibody therapy. Finding the optimal treatment approach therefore is pertinent. Here, we aimed to identify factors predicting response to second-line T-based therapy. Methods: 80 pts (median age 50.5 years) with ABC treated with >1 line of T-containing therapy were identified from a breast cancer database. HER-2-status was determined by immunohistochemistry (HercepTest) and re-analyzed by FISH if a score of 2+ was gained. Response rate (RR; CR+PR), clinical benefit rate (CBR; CR+PR+SD >6 months), time to progression (TTP), overall survival (OS), and cardiac toxicity were recorded. Response was evaluated every three months (m) using UICC criteria. TTP and OS were estimated using the Kaplan-Meier product limit method. In order to identify factors associated with TTP, the following variab...