[Subtype Change and Treatment Refractoriness at the Time of Recurrence in a Patient with Breast Cancer]

We present the case of a 54-year-old woman who was treated with preoperative chemotherapy, surgery, postoperative radiotherapy, and endocrine therapy for estrogen receptor(ER)-positive HER2-negative breast cancer. Positron emission tomography(PET)-computed tomography(CT)performed 10 years post-surgery revealed accumulation in the cervical and mediastinal lymph nodes and right chest wall. Endocrine therapy was initiated for the treatment of recurrent ER-positive and HER2-negative breast cancer but was unsuccessful. Despite initiation of chemotherapy, the patient developed bilateral recurrent nerve palsy and underwent tracheotomy. At the time of tracheotomy, biopsy evaluation revealed that the metastatic left supraclavicular lymph nodes were ER- and HER2-positive; therefore, the treatment was switched to a trastuzumab, pertuzumab, and docetaxel(TPD)combination for HER2-positive recurrent breast cancer. However, PET-CT revealed increased accumulation in the recurrent lesions, and the treatment was switched to trastuzumab deruxtecan (T-DXd). The accumulation of recurrent foci became less pronounced and the patient continued to progress without further deterioration.