Low concentrations of either endogenous or exogenous H2S promote tumour progression, mainly in the following ways: first, promoting angiogenesis by increasing the expression of VEGFR;21,22 second, promoting tumour growth by improving mitochondrial function in cancer cells;23 third, accelerating cancer cell cycle progression by modulating the phosphorylation of PKB/AKT and the action of extracellular signal-regulated kinase (ERK)24 and fourth, protecting against apoptosis in tumour cells by reducing intracellular ROS levels, thereby reducing mitochondrial disruption and DNA damage25. This evidence concerns the gene KDR and cancer.