[A case of trastuzumab-resistant breast cancer responding to lapatinib/capecitabine therapy].

: Here we report a case of a 56-year-old woman who presented at our hospital with a chief complaint of a red lump in her right breast. Breast cancer(Rt C, T4bN0M0; ER[-], PgR[-], HER2: 3[+]; stage IIIb)was diagnosed, and subsequent preoperative chemotherapy, mastectomy and axillary lymph node dissection were performed. Five months after surgery, bone metastasis in the thoracolumbar vertebrae developed and trastuzumab/zoledronic acid hydrate therapy was initiated. Four months after the therapy, tumor marker levels increased and docetaxel was added to the treatment regimen. Although the patient's condition temporarily improved, tumor marker levels increased again after 6 months, and the treatment regimen was switched to trastuzumab/nab-paclitaxel therapy. However, such regimen was discontinued owing to the development of liver metastasis, and lapatinib/capecitabine therapy was initiated. Two months after lapatinib/capecitabine therapy, tumor marker levels normalized and the liver metastasis markedly reduced. Side effects included paronychia(grade 3), which improved with dose reduction. The patient's therapy is being continued.