PLAU and neoplasm: Finally, modeling of the PAI-1 “cycle” (its expression/secretion as a soluble protein, deposition in the matrix, activity or latency, interactions with VN, “consumption” as part of a complex with uPAR and uPA and subsequent internalization) indicates that secreted PAI-1 by tumor cells is not homogeneously distributed at the tumor periphery, but rather localized in high-concentration deposits particularly in tumors characterized by the presence of invaginations [28].