Summary

A 55-year-old woman with metastatic human epidermal growth factor receptor 2 (HER-2) positive breast cancer (BC) to the lungs and bones was diagnosed with central nervous system (CNS) metastases in November 2011. The MRI showed a right parietal lobe mass with adjacent leptomeningeal disease and several small bilateral cerebellar metastases. She was treated with whole brain irradiation (WBI), followed by capecitabine and lapatinib (December 2011-March 2013) and trastuzumab and lapatinib (May 2013-August 2013). Then, the brain MRI showed progression. In the absence of significant neurological symptoms, we postponed WBI and closely monitored for the development of neurological symptoms. Systemic treatment with trastuzumab emtansine (T-DM1), an antibody-drug conjugate composed of the cytotoxic agent DM1 conjugated to trastuzumab, was initiated in September 2013 to control systemic disease. Unexpectedly, after two cycles of treatment the brain MRI showed a decrease in size of CNS metastases. This case report suggests possible activity of T-DM1 in HER-2 positive BC with CNS metastases.