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

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:

• ≥4 positive lymph nodes
• 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).

• 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.

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