PGR and breast cancer: Studies in the MCF-7 human breast cancer cell line have shown that fulvestrant significantly suppresses cellular levels of ER protein (McClelland et al, 1996a) and inhibits ER-induced expression of the progesterone receptor (PgR), the oestrogen-regulated protein pS2 and cathepsin D more strongly than tamoxifen (Nicholson et al, 1995a).