Comparing matched primary tumor and metastatic lesions revealed a significantly higher density of CD45+, CD3+, and CD8+ cell infiltration in lung metastases compared to primary tumors and liver metastases in mice transplanted with both A375 (6/6 mice) and MDA‐MB‐231 cells (3/3 mice; Fig. 2F–H), indicating that lung metastasis is particularly accessible for immune cells in HIS mice. This evidence concerns the gene CD8A and neoplasm.