366PACTIVITY OF T-DM1 IN HER2-POSITIVE BREAST CANCER BRAIN METASTASES.

Brain metastases (BM) are frequently diagnosed in metastatic Her2-positive breast cancer. Local treatment remains the standard of care but lapatinib plus capecitabine was recently established as systemic therapy option. Due to a disruption of the blood–brain/tumour-barrier at metastatic sites, even large molecules may penetrate into the central nervous system (CNS). Here, we report on the activity of T-DM1 in Her2-positive breast cancer BM. T-DM1 was administered at a dose of 3.6 mg once every 3 weeks as primary systemic therapy for BM or upon documented CNS progression after initial local treatment. Thus, this study allowed for the appraisal of T-DM1 activity in BM. Restaging was conducted every 12 weeks with MRI or whenever symptoms of disease progression occurred. Ten patients were included; in two asymptomatic subjects, T-DM1 was administered as primary therapy, while eight had progressive BM. All patients had received prior treatment with trastuzumab, six had already received lapatinib, and three pertuzumab as well. Three patients had partial remission of BM, and two patient had stable disease lasting for ≥6 months; two further patients had stable disease for <6 months while three progressed despite treatment. At 8.5 months median follow-up, intracranial PFS was 5 months, and median OS from initiation of T-DM1 was not reached. Local treatment of BM remains the standard of care; lapatinib plus capecitabine is currently the best established systemic therapy option. Still, T-DM1 apparently offers relevant clinical activity in BM and further investigation is warranted.