Mice deficient in several immune effector cells and molecules including interferon (IFN)-γ receptor or signal transducer and activator of transcription 1 (STAT1) [4], natural killer (NK) cells, NK-T cells [5, 6], γδ T cells [7, 8], IL-12 [9], perforin [10], and granulocyte-macrophage colony stimulating factor (GM-CSF) [11] have been demonstrated to be more susceptible to tumor development. This evidence concerns the gene CSF2 and neoplasm.