Although the importance of NK cells as a direct anti-tumor effector is well appreciated, the immuno-regulatory function of NK cells to control cancer-associated inflammation, which facilitate tumor progression, remains unknown. In this study, we demonstrate that the novel function of NK cells to control tumor-promoting inflammation through the functional modification of neutrophils. NK cells control the tumor-promoting function of neutrophils via an IFN-g-dependent mechanism and the tumor progression in an NK cell-depleted host is totally diminished when the IL-17A-neutrophils axis is absent. In NK cell-depleted mice, neutrophils acquire the tumor-promoting phenotype as seen in the up-regulation of VEGF-A expression to promote tumor growth and angiogenesis. Importantly, the systemic neutropenia by an antimetabolite treatment shows a significant anti-cancer effect only in mice with no NK cells. Thus, NK cells likely play an important role in controlling the tumor-promoting and angiogenic function of neutrophils. We are now further exploring tumor environment factors that modulate tumor-promoting function of neutrophils.