[A Case of Breast Cancer Brain Metastases Successfully Treated with Pembrolizumab Therapy after Disease Progression with Atezolizumab Therapy].

A 39-year-old woman was diagnosed with right breast cancer(cT3N1M0, cStage ⅢA, triple negative type). After preoperative chemotherapy using dose-dense doxorubicin and cyclophosphamide, followed by dose-dense paclitaxel every 2 weeks, the patient underwent right modified radical mastectomy. Postmastectomy radiotherapy to the right chest wall and right supraclavicular area and oral capecitabine therapy were administered. Computed tomography 1 year after surgery showed multiple lung metastases. The patient received atezolizumab and nab-paclitaxel therapy. Six months after the first chemotherapy, metastatic brain tumor in right frontal lobe, 12 mm in size, was observed along with enlargement of lung metastases. Because the brain tumor showed rapid growth after CyberKnife therapy, emergency tumorectomy was performed. One month after cranial surgery, new 3 brain metastases were appeared. Gamma knife therapy to brain metastases and pembrolizumab, carboplatin, gemcitabine therapy was started. Although insufficient doses of carboplatin and gemcitabine were administered due to bone marrow suppression, no progression was observed for about 1 year after initiation of pembrolizumab therapy. Pembrolizumab therapy may show anti-tumor effect to breast cancer brain metastases, even after a failure of atezolizumab therapy.