EFFECTS OF SHORT-TERM ANTIESTROGEN TREATMENT OF PRIMARY BREAST-CANCERON ESTROGEN-RECEPTOR MESSENGER-RNA AND PROTEIN EXPRESSION AND ON ESTROGEN-REGULATED GENES

Effects of the pure antiestrogen ICI182780 and tamoxifen on ER-protein , ER-mRNA, and estrogen-regulated mRNA expression were analysed using matched pretreatment core-cut biopsies and post-treatment mastectomy s amples from 43 ER positive human breast cancers, Sixteen controls rece ived either no preoperative treatment (n = 9) (7 days) or placebo (n = 7) (median 21 days) prior to primary surgery. Nineteen patients recei ved ICI182780 6 mg/day (n = 10) or 18 mg/day (n = 9) for 7 days. Eight patients were given preoperative tamoxifen (4 x 40 mg-day 1, 20 mg/da y thereafter, median 21 days). ER-protein expression was assessed on p re and post treatment samples by immunocytochemistry. ER, pS2, pLIV1, and actin-mRNA expression was determined by northern analysis on post- treatment samples only. ER-mRNA levels were similar to controls follow ing ICI182780 or tamoxifen treatment. However ER-protein levels were s ignificantly suppressed by ICI182780, particularly at the higher dosag e (p = 0.0013). Tamoxifen had no significant effect on ER-protein leve ls. The ER-mRNA and ER-protein contents of control tumors were linearl y related (Spearman r = 0.719, p = 0.006). A similar relationship betw een pretreatment protein and post ICI182780 treatment mRNA levels was observed (r = 0.652, p = 0.005). However, comparison of post ICI182780 treatment protein and mRNA results shows a loss of linearity through a reduction in protein without concurrent loss of mRNA (r = 0.28, p = 0.257). pS2 mRNA hybridization was lower in ICI182780 treated samples than controls (Mann-Whitney p = 0.035) but was unaffected by tamoxifen . pLIV1 mRNA hybridization was uninfluenced by either treatment. Short term exposure of breast tumors to ICI182780 appears to produce a grea ter inhibition of estrogen-induced transcriptional events than tamoxif en. These effects appear to occur without a concurrent reduction in ER mRNA levels.