This is a prospective, randomized, open-label, multicenter phase III study to explore chemotherapy omission in ER+/HER2-endocrine-sensitive breast cancer with 1-3 positive lymph nodes receiving extended (3 year) adjuvant abemaciclib

This is a prospective, randomized, open-label, multicenter phase III study to explore chemotherapy omission in estrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative endocrine-sensitive breast cancer with 1-3 positive lymph nodes receiving extended (3 year) adjuvant abemaciclib. In this study, patient eligible will be randomized into either endocrine drug plus 3-year adjuvant abemaciclib without chemotherapy or treatment of physician's choice (TPC).The safety and efficacy of each group will be assessed through invasive disease free survival (iDFS), disease-free survival (DFS), distant disease free survival (DDFS), overall survival (OS) and adverse effects (AE) as graded by Common Terminology Criteria for Adverse Events (CTCAE) 5.0.

Inclusion Criteria:

• women aged 18-80 years old;

• Patient has localized invasive breast carcinoma with1-3 positive lymph nodes, T1-T2，and is ER+/HER2- confirmed by histopathology after early breast cancer surgery#HER2-negative breast cancer (based on most recently analyzed biopsy) defined as a negative in situ hybridization test or an Immunohistochemistry (IHC) status of 0, 1+ or 2+. If IHC is 2+, a negative in situ hybridization (Fluorescence in situ hybridization (FISH), Chromogenic in situ hybridization (CISH) .

• ER≥50%

• Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1;

• Has adequate organ function meeting the following criteria: (1) adequate bone marrow function: hemoglobin ≥ 90 g/L (no blood transfusion within 14 days); absolute neutrophil count ≥ 1.5 x 109 /L; platelet count ≥ 100 * 109 /L; (2)adequate liver and kidney function: Alanine Aminotransferase (ALT) ≤ 3×upper limit of normal (ULN), Aspartate Aminotransferase (AST) ≤ 3×ULN, Total Bilirubin (TBIL)≤ 1.5×ULN, serum creatinine ≤

  1×ULN#and with endogenous creatinine clearance rate of >50 ml/min (Cockcroft-Gault formula).

• Participants voluntarily joined the study, has signed informed consent before any trial related activities are conducted, has good compliance and has agreed to follow-up.

Exclusion Criteria:

• Has received neoadjuvant therapy (include chemotherapy, targeted therapy, radiotherapy or endocrine therapy#;
• Has bilateral breast cancer;
• Has previous history of additional malignancy, with the exception of adequately treated basal cell carcinoma and cervical carcinoma in situ.
• Has metastatic (Stage 4) breast cancer;
• Has any ≥T3 lesion
• Is pregnant, is breast feeding women, or women of childbearing age who cannot practice effective contraceptives;
• Patients participating in other clinical trials at the same time;
• Has severe organ dysfunction (cardiopulmonary liver and kidney) insufficiency, left ventricular ejection fraction (LVEF) < 50% (cardiac ultrasound); severe cardio cerebral vascular disease within the 6 months previous of randomization (such as unstable angina, chronic heart failure, uncontrolled hypertension with blood pressure>150/90mmgh, myocardial infarction, or cerebral blood vessel); diabetic patients with poor blood glucose control; patients with severe hypertension;
• Has severe or uncontrolled infection;
• the researchers judged patients to be unsuitable for the study.