NOS1 and NOS3 are constitutive enzymes whereas NOS2 is inducible at the level of gene transcription and expressed by different types of cells, including cancer cells, in response to different factors, such as inflammatory cytokines (TNF-α; IL-1β, IFN-γ), endotoxins, heat shock protein Hsp70, hypoxia, and oxidative stress [24]. Here, TNF is linked to cancer.