Also, metformin treatment on patients with head and neck squamous cell carcinoma (HNSCC), esophageal squamous cell carcinoma (ESCC), colorectal cancer (CRC), or breast cancer has shown the enhanced infiltration of cytotoxic CD8+ TILs [26,27,28,29,30]. The gene discussed is CD8A; the disease is esophageal squamous cell carcinoma.