They can induce cellular proliferation, differentiation or cell death depending on the responding cell type and the microenvironment [7], for e.g., Fas/FasL interaction has been shown to be involved in neurogenesis [29]; the Fas/FasL system was also demonstrated to confer immune privileged status to tumor cells due to the expression of FasL on the tumor cells and the tumor endothelium [30,31], which induces cell death in the Fas-expressing T cells. The gene discussed is FAS; the disease is neoplasm.