This latter can take place through several ways: (1) through cell-to-cell contact (it is the most efficient), requiring the participation of anti-tumour antibodies and partly regulated by NO (nitric oxide) [245,246]; (2) due to several soluble factors (anti-tumour products secreted by macrophages) such as nitrite ion [245], TNF, Fas ligand (FasL or CD95L), hydrogen peroxide (H2O2) [233,245], iNOS (also known as NOS2) or high levels of MHC-II molecules [238]. The gene discussed is FASLG; the disease is neoplasm.