Chemotherapy Omission in ER+/HER2- Breast Cancer With 1-3 Positive Lymph Nodes Receiving Extended Adjuvant Abemaciclib

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 ≤
• ×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.