[Recurrent Breast Cancer with Pulmonary Lymphangitis Carcinomatosis Case Responding to Trastuzumab Deruxtecan].

Pulmonary lymphangitis carcinomatosis is generally characterized by resistance to chemotherapy and is associated with a poor prognosis. Herein, we present a case of pulmonary lymphangitic carcinomatosis from recurrent breast cancer that responded well to trastuzumab deruxtecan(T-DXd). The patient was a 40-year-old woman with hormone receptor-positive, HER2-positive breast cancer. At the age of 31, she had undergone a left mastectomy with axillary lymph node dissection. She received adjuvant chemotherapy(5-fluorouracil-epirubicin-cyclophosphamide, docetaxel, and trastuzumab)followed by endocrine therapy(tamoxifen and LH-RHa). Three years after the surgery, pulmonary and bone metastases were detected and she was treated with trastuzumab, pertuzumab, and capecitabine. Liver metastases were detected, and she was treated with trastuzumab emtansine. Nine years after surgery, the patient developed dyspnea and was diagnosed with lymphangitis carcinomatosis. After initiating T-DXd, dyspnea rapidly improved, and ground glass opacity on CT scan disappeared. She responded well to the treatment, with prolonged, stable disease for 1 year and 2 months. Thus, T-DXd may be effective against pulmonary lymphangitis carcinomatosis, which is generally characterized by resistance to chemotherapy.