The mechanisms underlying the radiation-enhancing effects of COX-2 inhibitors include (1) an accumulation of cells in the G2/M phases of the cell cycle which are considered to be sensitive to irradiation; (2) a reduction of PG-induced immunosuppressive activity caused by antitumor immunologic responses capable of potentiating tumor responses to radiation; and (3) direct effects on tumor neovascularization [7,30,31]. The gene discussed is PTGS2; the disease is neoplasm.