Efficacy and Safety of Fluzoparib Combined With Adjuvant Endocrine Therapy for HR+/HER2- SNF3-subtype Early Breast Cancer (BCTOP-L-A01)

Inclusion Criteria:

1. Women aged 18-70 years old;
2. ECOG score 0 or 1;
3. ER+/HER2- confirmed by histopathology after early breast cancer surgery（ER positive isdefined as immunohistochemistry(IHC) detection of ER ≥ 1% HER2-negative is defined asa negative in situ hybridization test or an IHC status of 0, 1+ or 2+. If IHC is 2+, anegative in situ hybridization (Fluorescence in situ hybridization (FISH), Chromogenicin situ hybridization (CISH) , or Silver in situ hybridization (SISH)) test isrequired by local laboratory testing.); definition of SNF3 subtype: SNF3 subtypeconfirmed by digital pathology of H&E sections;
4. Postoperative pathological stage T2-4N0-3M0;
5. Patients who have previously received neoadjuvant chemotherapy and/or adjuvantchemotherapy;
6. Time of randomization from surgery does not exceed 16 months;
7. Time of endocrine therapy from last non-endocrine anti-tumor treatment does not exceed 12 weeks;
8. Has adequate organ function meeting the following criteria: (1) adequate bone marrowfunction: hemoglobin ≥ 90 g/L (no blood transfusion within 14 days); absoluteneutrophil count ≥ 1.5 x 10^9 /L; platelet count ≥ 100 * 10^9 /L; (2)adequate liverand kidney function: Alanine Aminotransferase (ALT) ≤ 3×upper limit of normal (ULN),Aspartate Aminotransferase (AST) ≤ 3×ULN, Total Bilirubin (TBIL)≤ 1.5×ULN, serumcreatinine ≤ 1×ULN，and with endogenous creatinine clearance rate of >50 ml/min (Cockcroft-Gault formula);
9. Patients receiving radiotherapy must recover from the acute phase reaction ofradiotherapy, with a washout period of at least 14 days from the end of radiotherapyto randomization;
10. Patients who received chemotherapy in the early stage must recover from acute adversereactions to chemotherapy ([CTCAE] grade ≤ 1) before randomization, except for hairloss or grade 2 peripheral neuropathy. There is a washout period of at least 21 daysfrom the last chemotherapy administration to randomization (assuming the patient hasnot received radiotherapy);
11. Patients can take medication orally on their own;
12. Female subjects with fertility are required to use a medically approved contraceptivemethod during the study treatment
13. Participants voluntarily joined the study, has signed informed consent before anytrial related activities are conducted, has good compliance and has agreed tofollow-up.

Exclusion Criteria:

1. Has bilateral breast cancer;
2. Has previous history of additional malignancy, with the exception of adequatelytreated basal cell carcinoma and cervical carcinoma in situ.
3. Has metastatic (Stage 4) breast cancer;
4. Is pregnant, is breast feeding women, or women of childbearing age who cannot practiceeffective contraceptives;
5. Patients participating in other clinical trials at the same time;
6. Has severe organ dysfunction (cardiopulmonary liver and kidney) insufficiency, leftventricular ejection fraction (LVEF) < 50% (cardiac ultrasound); severe cardiocerebral vascular disease within the 6 months previous of randomization (such asunstable angina, chronic heart failure, uncontrolled hypertension with bloodpressure>150/90mmgh, myocardial infarction, or cerebral blood vessel); diabeticpatients with poor blood glucose control; patients with severe hypertension;
7. Has known allergy to fluzoparib and excipients.
8. Has severe or uncontrolled infection;
9. Has a history of psychotropic substance abuse and were unable to abandon drug habits,or those with history of mental disorders;
10. The researchers judged patients to be unsuitable for the study.