Chemotherapy Omission in HR-positive/HER2-negative Breast Cancer With Lymph Node Negative Disease Receiving Adjuvant Endocrine Therapy and CDK4/6 Inhibitor

Inclusion Criteria: * Females and males aged 18-70 years; * ECOG performance status 0-1; * Early-stage breast cancer, with postoperative pathology confirming invasive carcinoma, HR-positive and HER2-negative (In this study, HR-positive is defined as: ER-positive by IHC with \>10% tumor cells staining positive; HER2-negative defined as HER2 0-1+ by IHC or HER2++ with negative FISH result, without amplification); * Postoperative pathological stage pT2N0M0 and: Histological grade 3, or Histological grade 2 with Ki67 ≥ 20% or high-risk multigene assay results; * No prior neoadjuvant therapy received; * Good postoperative recovery, with randomization occurring no more than 8 weeks after surgery; * Normal function of major organs, meeting the following criteria: Hematological tests must meet: HB ≥90 g/L (no transfusion within 14 days); ANC ≥1.5×10⁹/L; PLT ≥100×10⁹/L; Biochemical tests must meet: TBIL ≤1.5×ULN (upper limit of normal); ALT and AST ≤3×ULN; serum Cr ≤1.5×ULN; * Contraception required for male participants and women of childbearing potential during treatment; * Participants voluntarily enroll in the study, sign informed consent, demonstrate good compliance, and cooperate with follow-up. Exclusion Criteria: * Bilateral breast cancer or carcinoma in situ (DCIS/LCIS); * Metastasis at any site; * Clinical or imaging suspicion of malignancy in the contralateral breast requiring biopsy (unless ruled out); * Prior neoadjuvant therapy, including chemotherapy, radiotherapy, or endocrine therapy; * Use of tamoxifen, raloxifene, or aromatase inhibitors (AIs) for breast cancer risk reduction ("chemoprevention") and/or osteoporosis treatment within the past 2 years; * History of other malignancies within the past 5 years (except basal cell carcinoma of the skin or carcinoma in situ of the cervix), including contralateral breast cancer; * Concurrent participation in another clinical trial; * Severe systemic diseases and/or uncontrolled infections that preclude study participation; * Severe cardiovascular or cerebrovascular events within 6 months before randomization (e.g., unstable angina, chronic heart failure, uncontrolled hypertension \>150/90 mmHg, myocardial infarction, or stroke); * Known hypersensitivity to the study drugs; * Men and women of childbearing potential unwilling to use contraception during treatment and for 8 weeks after treatment completion; * Pregnant or lactating women; * Positive pregnancy test before study drug administration (for women of childbearing potential); * Psychiatric disorders, cognitive impairment, or inability to comprehend the trial protocol, adverse effects, or comply with study procedures and follow-up (requires systematic evaluation before enrollment); * Individuals lacking personal freedom or legal capacity for independent civil conduct.