ROS formation triggers cell proliferation, so all together features of MDR1-overexpressing cancer cells create a vicious circle where increased ROS formation and iNOS expression enhance cancer cell proliferation, leading to hypoxia that causes secretion of VEGF, hepatocyte growth factor and the hypoxia inducible factor with the contemporary enhancement of the MDR1 gene transcription 17,21. Here, NOS2 is linked to cancer.