High-grade fetal lung adenocarcinoma (H-FLAC) is a rare tumor, with little known of its response to chemotherapy with or without an immune checkpoint inhibitor or of its molecular profile. We report the first case of a 56-year-old man with stage IV H-FLAC who was successfully treated with carboplatin plus nab-paclitaxel in combination with atezolizumab. In addition, the tumor was found to be positive for amplification of the human epidermal growth factor receptor 2 gene.