The signals inducing expansion are primarily factors produced by tumor cells and include growth factors and cytokines, such as granulocyte-macrophage colony-stimulating factor (GM-CSF) [39,40], granulocyte colony-stimulating factor (G-CSF) [41], macrophage colony-stimulating factor (M-CSF) [42], IL-6 [43], vascular endothelial growth factor (VEGF) [44], stem cell factor (SCF) [45], and prostaglandins [46,47]. Here, KITLG is linked to neoplasm.