TNF and neoplasm: Natural killer (NK) cells are a crucial component of the innate immune system, which can destroy tumor cells without previous sensitization, as well as the production of immunoregulatory cytokines early in an immune response (Trinchieri, 1989; Biron et al., 1999), particularly interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF) (Yokoyama, 1999).