PGR and breast cancer: All these findings taken together seem to indicate that our tumours expressing both uPA–PAI-1 complexes and progesterone receptors are probably the ones also expressing the highest levels of PAI-1, with its inherent bad prognosis, and also showing the highest activity of the uPAR–uPA–PAI-1 system, with its promigratory, metastasis-enhancing effect on breast cancer cells.