KDR and neoplasm: 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.