Expression data from MCF7 wt xenografts

To investigate molecular mechanisms of resistance, we used two different in vivo xenograft models of estrogen receptor-positive (ER+) breast cancer, with or without HER2 over-expression (MCF7/HER2-18 and MCF7 wt, respectively). Mice with established tumors were assigned to the following treatment groups: continued estrogen supplementation (E2), estrogen deprivation (ED), ED plus tamoxifen (Tam), all with or without the EGFR tyrosine kinase inhibitor gefinitinib (G). Another group received ED plus the antiestrogen fulvestrant (MCF7 wt only). Tumors with acquired or de novo resistance to these endocrine therapies were profiled for mRNA expression using Affymetrix Genechip arrays. Keywords: multiple group comparison MCF7 xenografts were established in ovariectomized five to six week-old nu/nu athymic nude mice supplemented with 0.25 mg 21 day release estrogen pellets by inoculating subcutaneously (s.c.) 5E-6 cells. When tumors reached the size of 150-200 mm3 (3-5 weeks), the animals were randomly allocated to continued estrogen (E2), continued estrogen with gefitinib (E2+G; 100mg/kg, 5 days/week), estrogen withdrawal alone (ED; by removal of the estrogen pellets), and estrogen withdrawal plus tamoxifen citrate (Tam; 500 microg/animal s.c. in peanut oil, 5 days/week), with either gefitinib (Tam+G; 100mg/kg, 5 days/week) or vehicle (1% Tween 80) administered via gavage, as well as estrogen withdrawal plus fulvestrant (ICI 182,780) in the MCF7 wt model (Fulv; 5mg/mouse s.c. once weekly), and estrogen withdrawal with gefitinib (ED+G). Tumors were harvested for molecular studies when they became resistant to treatment and reached the size of 1000 mm3 (n=7).