ANPEP and neoplasm: In endothelial cells, CD13 mRNA and protein expression can be transcriptionally upregulated in response to diverse factors influencing the tumour microenvironment, such as hypoxia and increased presence of angiogenic growth factors such as bFGF, VEGF, tumour necrosis factor α (TNFα) and insulin-like growth factor-1 (IGF-1) (Bhagwat et al, 2001).