Tumor bearing animals were dosed with vehicle, tamoxifen (120 mg/kg/day p.o.), fulvestrant (200 mg/kg, 3x/week, s.c.)or GDC-0810 (10, 30 or 100 mg/kg/day, p.o.)for 27 days (B) Representative images of IHC for ERα and Ki67 in tamoxifen-resistant MCF7 xenograft tumors from (A) treated with vehicle, tamoxifen or GDC-0810. Here, ESR1 is linked to neoplasm.