Formal assessment of RAD001 combination index. Cell lines were treated as described with IC50 concentrations of each drug alone or in combination, as indicated in the graphs. For Combination Index Tables shown, each graph MCF7-AROM1 (A, B) and BT474-AROM3 (C, D) were treated over a 6-day period in the presence of 10 nM androstendione with equipotent doses of letrozole, 4-OH tamoxifen, and RAD001. In the case of LTED cells (E), similar analyses were carried out in the presence of E2 (0.01 nM), RAD001, and 4-OH tamoxifen at fixed ratios of the two agents. CIs were derived by using Calcusyn software, and significance was calculated as detailed in Methods.