Retreatment with trastuzumab (T)-based therapy in patients (pts) with HER2-positive (HER2+) metastatic breast cancer (MBC) resistant to lapatinib (L)-based therapy.

568 Background: Preclinical data suggest that treatment with lapatinib may reinduce sensitivity to trastuzumab in HER2+ breast cancer cells (Scaltriti, Oncogene 2009;28:803). We evaluated the activity of retreatment with T-based therapy after L in HER2+ MBC pts. Methods: 69 HER2+ MBC pts retreated with T after L progression were identified using pharmacy records from 9 Italian Institutions (Jan 2007-Nov 2010). Response to T retreatment, post-T progression-free survival (PFS) and overall survival (OS) were evaluated. Results: Pts median age was 57 y (26-79); ECOG PS was 0-1 in 77% (53/69), 2 in 7% (5/69) and not registered for 16% (11/69) of the pts; 51 pts (74%) had visceral metastases and 16 (23%) brain metastases with or without visceral involvement. All pts were pretreated with both T- and L-based therapy for MBC, and 11 had also received adjuvant T. The median number of chemotherapeutic lines for MBC before L was 2 (range 0-8) including a median of 2 (0-6) T-based regimens. The median duration of L wa...