Tumor-infiltrating T cells are the most relevant population of tumor-infiltrating lymphocytes and are found in most solid tumors (e.g., breast and colon cancer, melanoma, and neuroblastoma), where they play a crucial role in either favoring (by regulatory T cells) or inhibiting (by CD8+ T cells and CD4+ conventional T cells) tumor development [7,8,9,10,11]. The gene discussed is CD8A; the disease is neoplasm.