PGR and breast cancer: Mice harbouring the whey acidic protein WAP-HGF transgenic construct show elevated HGF expression in mammary epithelium, compared with wild-type mice, and go on to develop mammary tumours characterised by a high Ki67 proliferation index, a reduced progesterone receptor immunoreactivity and areas of squamous differentiation (a feature of BL breast cancers) [80,84].