The paradox of Th17 cell functions in tumor immunity

•Th17 cells produce high level of IL-17 that have close association with tumorigenesis.•IL-17 cytokines are double-edged agents and depending on type of cancer can be as anti- and pro-tumor cytokines.•Th17 cells may mediate protective anti-tumor immunity.•IL-17A is well-known to stimulate angiogenesis in tumor context.•Th17 cells and Th17-related cytokines have been exposed to have both anti-tumorigenic and pro-tumorigenic roles. Immune system acts as a host defensive mechanism protecting against attacking pathogens and transformed cells, including cancer cells. Th17 cells are a specific subset of T helper lymphocytes determined by high secretion of IL-17 and other inflammatory cytokines. Th17 cells increase tumor progression by activating angiogenesis and immunosuppressive activities. They can also mediate antitumor immune responses through recruiting immune cells into tumors, stimulating effector CD8+ T cells, or surprisingly by altering toward Th1 phenotype and producing IFN-γ, so Th17 cells are supposed as a double-edged sword in cancer. A comprehensive approach to indicating the activity of Th17 cells in tumor progression could help in the planning of new therapeutic approaches specially targeting Th17 cells in cancer.