Chemotherapy Exemption in Elderly Women With Node-Positive ER+/HER2- Breast Cancer (ELDER)

Inclusion Criteria:

- 1. Age: Female patients aged ≥65 years. 2. Disease Status: Histologically confirmed early-stage breast cancer after surgery with ER expression ≥50% AND one of the following:

1. ≥4 positive lymph nodes
2. 1-3 positive lymph nodes plus at least one of the following high-risk features: i. High-risk multigene assay result ii. Primary tumor size >2 cm iii. Histologic grade 3 iv. Lymphovascular invasion (LVI) positive v. Ki-67 >20% 3. Treatment Acceptance: Willing to receive adjuvant CDK4/6 inhibitor therapy. 4. Performance Status: ECOG score 0-2. 5. Adequate Organ Function:

a) Hematology (within 14 days, no transfusion): i. Hemoglobin (Hb) ≥90 g/L ii. Absolute neutrophil count (ANC) ≥1.5×10⁹/L iii. Platelets (PLT) ≥100×10⁹/L b) Biochemistry: i. Total bilirubin (TBIL) ≤1.5×ULN ii. ALT/AST ≤3×ULN iii. Serum creatinine (Cr) ≤1×ULN iv. Estimated creatinine clearance (CrCl) >50 mL/min (Cockcroft-Gault formula) 6. Consent & Compliance: Willing to participate, sign informed consent, and comply with follow-up.

Exclusion Criteria:

• Patients who have received neoadjuvant therapy (including chemotherapy, targeted therapy, radiotherapy, or endocrine therapy).

  2. Bilateral breast cancer. 3. History of other malignancies, except: Cured basal cell carcinoma of the skin； Carcinoma in situ of the cervix 4. Distant metastasis (any site). 5. Any T4 lesion (UICC 1987 TNM staging), including: Skin invasion; Fixed mass adherence; Inflammatory breast cancer 6. Concurrent participation in other clinical trials. 7. Severe organ dysfunction (cardiac, pulmonary, hepatic, or renal), including:

  a) LVEF <50% (by echocardiography) b) Major cardiovascular/cerebrovascular events within 6 months before randomization: i. Unstable angina ii. Chronic heart failure iii. Uncontrolled hypertension (>150/90 mmHg) iv. Myocardial infarction or stroke c) Poorly controlled diabetes mellitus d) Severe hypertension 8. Known allergy to taxane-based drugs or their excipients. 9. Severe or uncontrolled infections. 10. History of psychoactive drug abuse (unable to abstain) or psychiatric disorders.

  11. Patients deemed ineligible by investigator assessment. 12. Refusal to receive adjuvant CDK4/6 inhibitor therapy.