Response to Dabrafenib and Trametinib of a Patient withMetaplastic Breast Carcinoma Harboring a BRAF V600E Mutation

Metaplastic breast carcinomas are rare and carry poor prognoses. They are also more aggressive than other breastcancers and are known for their resistance to chemotherapy. Prolonged treatment with dabrafenib and trametinib is a therapyfor malignant melanoma that improves the progression-free survival and overall survival. Such molecular-targeted therapies arealso being developed for cancers with BRAF mutation, a driver of malignant melanoma.Case Presentation. A 57-year-oldwoman with metaplastic breast cancer and chemotherapy-refractory massive pleural effusion. After contained anthracyclineregimen failure, her breast cancer progressed to an advanced stage. We ordered next-generation sequencing- (NGS-) basedtumor molecular profiling from core needle biopsy of the breast. The NGS report indicated the presence of a BRAF V600Emutation. After initiation of dabrafenib and trametinib, her symptom and the pleural effusion were decreased. Thefirstassessment of CT scans showed a decreased pleural effusion and shrunken subcutaneous lesions. Approximately 2 weeks later, anew lesion appeared. She died from 12 weeks after initiation of dabrafenib and trametinib treatment.Conclusion. To the best ofour knowledge, this is thefirst report of BRAF mutation breast cancer treated with dabrafenib and trametinib and it heralds thepossibility of targeted therapy for rare breast cancers.