Effect of fulvestrant on ER signalling and growth in MCF-7, T47D, BT474 and MDAMB361 cells. Western blotting and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis demonstrating effect of a seven-day incubation of MCF-7, T47D, BT474 and MDAMB361 cells with either fulvestrant (100 nM) or vehicle control (ethanol) on (A) oestrogen receptor α (ERα) protein and (B) progesterone receptor (PgR) mRNA, β-actin mRNAand cyclin D1 protein expression. For each cell line, PgR mRNA expression is shown as upper band and β-actin mRNA as lower band on RT-PCR image. Data are representative of at least three separate experiments. β-actin protein expression was also assessed for all Western blotting studies (data not shown) to confirm equivalent sample loading. (C) Effects of increasing concentrations of fulvestrant (0.01 to 1 μM) on the basal growth of MCF-7, T47D, BT474 and MDAMB361 cells on day 7 after initial treatment. The results are expressed as means ± SEM of triplicate wells and are representative of three separate experiments. *P < 0.05 versus control (0), **P < 0.01 versus control (0), ***P < 0.001 versus control (0).