Dalpiciclib Combined With Letrozole in Neoadjuvant Treatment of Stage Ⅱ-Ⅲ HR-positive/HER2-negative Breast Cancer

Inclusion Criteria: * 1\. Postmenopausal women aged ≥18 years, the definition of postmenopausal: 1. the patients with the history of bilateral oophorectomy, or age ≥ 60 years; or 2. Age \<60, natural postmenopausal state (defined as the spontaneous cessation of regular menstruation for at least 12 consecutive months, without other pathological or physiological causes), E2 and FSH at the postmenopausal levels 2. All patients were estrogen receptor (ER) positive (\>10%), HER2 -negative invasive breast cancer regardless of PR expression level. Immunohistochemistry (IHC) score of 0+, or 2+ confirmed by pathology laboratory and negative in situ hybridization (ISH) test (HER-2/CEP17 ratio \<2.0); 3. Treatment-naive patients with stage Ⅱ-Ⅲ tumors whose tumor staging meets the criteria of the 8th edition of the American Joint Committee on Cancer (AJCC) Staging; Exclusion Criteria: * 1\. Received any form of anti-tumor therapy (chemotherapy, radiotherapy, molecular targeted therapy, endocrine therapy, etc.) 2. Concurrently receiving any other anti-tumor therapy that those specified in the protocol; 3. Bilateral breast cancer, inflammatory breast cancer, or occult breast cancer; 4. Stage Ⅳ breast cancer;