Here, we report a rare case of an elderly non-smoking female patient presenting with lung adenocarcinoma of unknown primary with extensive lymph node metastases and massive malignant pleural and pericardial effusions, harboring a BRAF V600E mutation and high PD-L1 expression, who exhibited a remarkable response to combined dabrafenib, trametinib and pembrolizumab therapy. Here, CD274 is linked to lung adenocarcinoma.