Improved clinical and cell cycle response with an mTOR inhibitor, daily oral RAD001 (everolimus) plus letrozole versus placebo plus letrozole in a randomized phase II neoadjuvant trial in ER+ breast cancer

530 Background: Activation of the mTOR pathway is a key adaptive change driving endocrine resistance. RAD001, an oral mTOR inhibitor, and letrozole synergistically inhibit proliferation in breast cancer cells. Methods: 270 postmenopausal women with > T2 ER+ tumors were randomized to receive 4 mo of letrozole 2.5mg QD + RAD001 10mg QD or letrozole 2.5mg plus placebo. The primary endpoint was overall clinical response. Mandatory needle biopsies were collected immediately prior to initial treatment, and at day 15 after treatment initiation. Samples were assessed at baseline for Her2 by FISH and mutation of exons 9 and 20 of PIK3CA and exons 5–8 of TP53, and at baseline and day 15 for Ki67, phospho-Akt S473, phospho-S6, PTEN, CyclinD1, ER, PR, p53, and total Akt and S6 by immunohistochemistry. A total of 207 patients (77%) were primary marker evaluable and clinical outcome evaluable; 186 patients had an evaluable second biopsy. Results: The clinical response rate with RAD001 + letrozole was significantly supe...