Could 2 years of hormone therapy be enough for some breast cancers?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Females aged 18 years or older; * Postoperative pathological stage I early breast cancer: histologically confirmed invasive carcinoma with a maximum diameter ≤2 cm and node-negative (N0); * Immunohistochemistry (IHC) shows ER-positive (ER ≥50%), HER2 IHC score of 0, 1+, or 2+ with no amplification confirmed by FISH, and Ki-67 ≤20%; * Presence of at least one of the following potential low-risk factors: 1）Tumor size ≤1 cm, 2）21-gene recurrence score \<11, 3）Fudan digital pathological subtype classified as SNF1, 4）Age ≥65 years; * ECOG performance status of 0 or 1; * Patients with bilateral synchronous invasive lesions are eligible if both lesions are ER-positive, HER2-negative, and meet the tumor size criteria; * Normal major organ function, meeting the following criteria: 1. Hematological: HB ≥90 g/L (no transfusion within 14 days), ANC ≥1.5×10⁹/L, PLT ≥100×10⁹/L; 2. Biochemical: TBIL ≤1.5×ULN, ALT and AST ≤3×ULN, serum Cr ≤1×ULN, and creatinine clearance \>50 mL/min (Cockcroft-Gault formula); * Participants voluntarily enroll, sign informed consent, demonstrate good compliance, and cooperate with follow-up. Exclusion Criteria: * Primary tumor size \>2 cm in maximum diameter and/or axillary lymph node positivity; * Prior neoadjuvant therapy, any systemic therapy, or local therapy (except surgery), including chemotherapy, targeted therapy, radiotherapy, or endocrine therapy; * Prior adjuvant chemotherapy; * Use of CDK4/6 inhibitors in the adjuvant setting; * History of other malignancies (except cured basal cell carcinoma or cervical carcinoma in situ); * Metastasis at any site; * Pregnancy, lactation, or women of childbearing potential unable to use effective contraception; * Concurrent participation in other clinical trials; * Severe cardiac, pulmonary, hepatic, or renal dysfunction; LVEF \<50% (by echocardiography); severe cardio-cerebrovascular diseases within 6 months (e.g., unstable angina, chronic heart failure, uncontrolled hypertension \>150/90 mmHg, myocardial infarction, or stroke); poorly controlled diabetes; severe hypertension; * Severe or uncontrolled infections; * History of drug abuse or psychiatric disorders; * Patients deemed unsuitable for the study by the investigator.