Because CD8+ T cells also express TRAIL (Fig. 5C), the function of tumor-specific CD8+ T cells can be two folds: first, CD8+ T cells may infiltrate inside tumor (Fig. 6Aa b&d) and utilize IFN-γ, TNFα and TRAIL to induce tumor cell apoptosis; second, CD8+ T cells may not effectively infiltrate the advanced tumor, especially the metastatic tumor (Fig. 6A, c&e), however, the activated CD8+ T cells can still secrete IFN-γ and TNFα. This evidence concerns the gene CD8A and metastatic neoplasm.