Abstract
Gastric and oesophageal cancers (GOCs) are lethal cancers which metastasise early and recur frequently, even after definitive surgery. The urokinase plasminogen activator system (uPAS) is strongly implicated in the invasion and metastasis of many aggressive tumours including GOCs. Urokinase plasminogen activator (uPA) interaction with its receptor, urokinase plasminogen activator receptor (uPAR), leads to proteolytic activation of plasminogen to plasmin, a broad-spectrum protease which enables tumour cell invasion and dissemination to distant sites. uPA, uPAR and the plasminogen activator inhibitor type 1 (PAI-1) are overexpressed in some GOCs. Accumulating evidence points to a causal role of activated receptor tyrosine kinase pathways enhancing uPAS expression in GOCs. Expression of these components are associated with poorer clinicopathological features and patient survival. Stromal cells, including tumour-associated macrophages and myofibroblasts, also express the key uPAS proteins, supporting the argument of stromal involvement in GOC progression and adverse effect on patient survival. uPAS proteins can be detected on circulating leucocytes, circulating tumour cells and within the serum; all have the potential to be developed into circulating biomarkers of GOC. Herein, we review the experimental and clinical evidence supporting uPAS expression as clinical biomarker in GOC, with the goal of developing targeted therapeutics against the uPAS.