Treatment and outcome of metastatic HER2-positive breast cancer relapsing post adjuvant trastuzumab exposure.

1080 Background: Since 2006 adjuvant trastuzumab (AT) has been standard care for HER2 +ve early breast cancer (BC) treated with chemotherapy (CT). No data exists on the response and benefit of subsequent treatment, including trastuzumab (T) re-exposure, in cases developing recurrent disease following AT. Methods: All cases of early HER2 +ve BC exposed to AT at our institutions were reviewed and cases of recurrent/metastatic disease identified. Clinicopathological and adjuvant treatment details in recurrent cases were recorded. Sites of relapse, treatment, and details of further T based therapy were recorded. Response to treatment and outcome were analyzed. Results: 284 cases were identified who had received ≥1 dose of AT and 29relapses recorded (Local recurrence: 13.8%; distant recurrence: 86.2%). 34.5% received adjuvant CT and 65.5% neoadjuvant (NA) CT, 2 received NA T. Median time to relapse from diagnosis was 18.3 months (m) (range 9.2-48.2) and 8.5m (range 1.4-40.0) from AT initiation. 55% of relapses...