Other arguments in favor of an involvement of active mechanisms in the initial steps of metastasis include the accumulation of mutations, changes in the expression of adhesion molecules, the presence of chemokine gradients, expression of the urokinase plasminogen activator (uPA) followed by activation of metalloproteinases (MMPs), and the supportive role of stromal cells and cancer-associated fibroblasts, CAFs [24]. The gene discussed is PLAU; the disease is cancer.