Mice (n=7–9/group) bearing (B) MCF-7 tumors, (C) T47D/FR tumors, or (D) HCI-003 patient-derived xenografts were treated as indicated in (A). In (C), mice were treated with fulv starting at the time of xenografting, and fulv was stopped after 6.5 wk of GDC-0941/fulv treatment. Mean + SEM is shown. *p≤0.05 compared to vehicle-treated group, or as indicated with brackets. #p≤0.05 compared to fulvestrant-treated group. &p≤0.05 compared to GDC-0941-treated group at same dose/schedule. Statistical analysis of (B) included data up to 6.5 wk.