NOS2 and neoplasm: The results of the study in which chemotherapy with 5-fluorouracil (5-FU), together with supplementation of the NO precursor L-arginine (L-Arg), was administered to a nude mice model of human liver cancer revealed that 5-FU could induce an increase in the expression and activity of iNOS in vivo, and after combination with L-Arg 5-FU could significantly enhance the expression and activity of iNOS and significantly increase the concentration of NO in tumor tissues, suggesting that endogenous NO plays an important role in the in vivo antitumor effect of 5-FU combined with L-Arg [9].