This open, randomized pilot feasibility trial is to evaluate the feasibility and effect of neoadjuvant everolimus plus letrozole versus neoadjuvant fluorouracil, epirubicin plus cyclophosphamide (FEC) in treating postmenopausal women with ER-positive, HER2-negative breast cancer. Forty postmenopausal stage M0, ER-positive, HER2-negative invasive breast cancer women who had a primary tumor > 2cm by imaging or an axillary lymph node > 2cm by imaging were randomly (1:1) enrolled to receive neoadjuvant everolimus plus letrozole for 18 weeks or neoadjuvant FEC for 6 cycles before surgery. The primary objective is to determine the feasibility of neoadjuvant everolimus plus letrozole in postmenopausal patients with ER-positive, HER2-negative breast cancer, and to compare the objective response rate. Secondary aims are to compare the response rate by clinical palpation, pathological complete response (pCR) rate, breast-conserving surgery rate, toxicities, and changes in the percentages of peripheral blood CD8+ T cells, T helper cells (Th), regulatory T cells (Treg), and NK cells (pre- versus post- neoadjuvant therapy).