We formed brain metastases by transplanting syngeneic mouse tumor cells via the internal carotid artery, elucidated the antitumor efficacy of the combined use of anti-PD-L1 and anti-VEGF antibodies on established brain metastases in immune-competent mice, and performed an examination of the immune cells within the brain metastases and the associated lymph nodes, as well as an assessment of the tumor blood vessel density. Here, CD274 is linked to neoplasm.