Excellent Response with Ado-Trastuzumab Emtansine in a Patient with Relapsed Metastatic Breast Cancer Presenting with Pulmonary Lymphangitic Carcinomatosis.

In breast cancer, aggressive tumor biology and the corresponding poor prognosis is associated with amplification or overexpression of the human epidermal growth factor receptor 2 (HER2). Trastuzumab has significantly changed the natural history of HER2-positive breast cancer. However, resistance to trastuzumab remains a substantial clinical problem. Ado-trastuzumab emtansine (T-DM1), an antibody-drug conjugate, has demonstrated impressive results in second- or later-line treatment of HER2-positive breast cancer. We report a case of 43-year-old female with previously trastuzumab-treated HER2-positive breast cancer relapsed with pulmonary lymphangitis carcinomatosis that responded dramatically to T-DM1 therapy.