Complete response in a patient with metastatic metaplastic breast cancer treated with immune checkpoint inhibitor and chemotherapy: A case report and a review of the literature.

Metaplastic breast cancer (MpBC) is a rare subtype of breast cancer characterized by poor prognosis and lack of treatment guidance. It is notably resistant to conventional chemotherapy. Currently, immunotherapy is becoming a promising option for multiple tumor types, including triple-negative breast cancer. This report presents a case of triple-negative MpBC that achieved a complete response with a combination of chemotherapy and immune checkpoint inhibitors. We examined the tumor's imaging and histological features, along with the treatment regimen and efficacy. Notably, no major toxicities related to immunotherapy were observed. To our knowledge, this is the first case report demonstrating the effectiveness of lambrolizumab in combination with the GP chemotherapy regimen for treating triple-negative breast cancer in general and specifically metastatic MpBC.