Molecular effects of anastrozole (A) and tamoxifen (T) alone and combined (C) in the IMPACT trial of neoadjuvant treatment of primary breast cancer

537 Background: Aromatase inhibitors and tamoxifen are key agents for endocrine treatment of postmenopausal breast cancer (BrCa). Understanding of their molecular/biological effects in BrCa is needed for their rational application alone or in combination with novel therapeutics. Methods: 330 postmenopausal patients with invasive BrCa (>/=2cm) were randomised to 12wks neoadjuvant therapy with A, T or C in a placebo-controlled double-blind trial (IMPACT). Biopsies were available from a total of 292 patients pre-treatment and at 2 and 12 wks. Immunohistochemical (IC) studies were performed for Ki67, apoptosis (TUNEL), ER, PgR, EGFR (pre) and HER2 (pre). The growth index (GI: Ki67/apoptosis) was calculated. Plasma estradiol (E2) levels were measured. Results: The %age changes in the biomarkers from baseline are shown in the table. IC results for T and C were similar in all respects. The greater reductions in Ki67 in A vs T have been reported. There were greater reductions in GI for A vs T despite the decrease...