PGR and neoplasm: Similarly, in MCF-7 tumour xenografts, fulvestrant has also been shown to be more effective than tamoxifen in reducing cellular levels of the ER and PgR; expression levels of other oestrogen-regulated genes pLIV1 and pS2 were also greatly reduced (Osborne et al, 1994,Osborne et al, 1994, 1995).