Stromal cells directly participate in the establishment of the malignant, i.e. invasive, phenotype. This receptor is highly expressed in human tumour by both stromal and tumour cells. The abundance of UPAr signals an unfavourable prognosis. In murine model systems block of UPAr strongly reduces or abolishes the ability of tumours to spread, thus, this molecule is now an important target for drug design. Tumour cells activate their own migration by producing a cell-surface bound chemotactic activity.
Stromal cells recruit cancer cells by producing soluble chemoattracting molecules.