Non-small Cell Lung Cancer With Proto-Oncogene B-Raf V600E Presenting a Distinctive Clinical Course: A Case Report

Cases of proto-oncogene B-Raf (BRAF) V600E mutation are rare, accounting for 1%-4% of non-small cell lung cancers (NSCLCs), and its clinical features remain unclear. Here, we report a case of BRAF mutation-positive lung adenocarcinoma with an atypical clinical course and long-term survival. The patient was a 63-year-old female nonsmoker who was diagnosed with stage IA adenocarcinoma after surgical resection. Five years after the surgery, cancer recurred and was treated with various cytotoxic anticancer agents. During the course of treatment, the patient was found to be BRAF V600E mutation-positive and was treated with molecular-targeted drugs. Although multiple brain, subcutaneous, and tonsillar metastases appeared, the progression was significantly slower, and the patient survived for 14 years and three months after the diagnosis. There have been few case reports of long-term survival in BRAF-positive lung cancer, and more cases need to be accumulated in the future to gather more information. Based on this case, we speculate that sensitivity to cytotoxic anticancer agents such as pemetrexed (PEM) and maintenance of performance status (PS), in addition to molecular-targeted agents, are important for long-term survival.