It has been 10 years since the first report on the antitumor activity of IL-27 against a murine tumor model of colon carcinoma C26, which suggested that IL-27 has potent abilities to induce tumor-specific antitumor activity and protective immunity and that the antitumor activity is mediated mainly through CD8+ T cells, IFN-γ, and T-bet but not through STAT4 [24]. This evidence concerns the gene STAT4 and neoplasm.