APLN and cancer: A potential candidate, however, is apelin, a peptide ligand for the apelin receptor (APJ), which, when activated, regulates blood pressure and encourages the formation of new blood vessels.141 The expression of apelin is driven by hypoxia and hence is comparably high in cancers.142 Low apelin mRNA or protein serum levels were shown to indicate vessel normalisation in the mouse model; here, the lowest apelin levels were seen around day 5 after treatment, suggesting a normalisation window between days 3 and 5.143