Complete Response of Triple-Negative Metaplastic Carcinoma of the Breast Using Pembrolizumab

Metaplastic breast cancer (MpBC) is a rare form of breast malignancy with a poor prognosis and limited treatment guidance. Here, we report on a case of triple-negative MpBC that was successfully treated following the Keynote-522 clinical algorithm using pembrolizumab, paclitaxel, carboplatin, adriamycin, and cyclophosphamide in a neo-adjuvant fashion. The radiographic and histologic findings of the tumor are reviewed here along with the treatment regimen and response. No major toxicities associated with pembrolizumab were observed in this case. This case report serves as an example of complete pathological response of triple-negative MpBC with pembrolizumab plus chemotherapy and demonstrates the need for further research on chemoimmunotherapy for MpBC.