This study is planned to include 40 patients with HER2-negative advanced breast cancer to receive fluzoparib combined with chidamide or fluzoparib combined with camrelizumab to observe and evaluate the efficacy and safety of fluzoparib combined with camrelizumab or chidamide in the treatment of HRD-positive HER2-negative advanced breast cancer.

Inclusion Criteria:

1. histologically confirmed initial stage IV breast cancer or recurrent metastatic breast cancer; advanced treatment stage received at least 1 line of chemotherapy but no more than 2 lines of chemotherapy; hormone receptor-positive patients received at least one endocrine therapy in advanced treatment stage, or the investigator judged that they were not suitable for endocrine therapy; and patients with hormone receptor-positive advanced breast cancer who progressed within 2 years of adjuvant endocrine therapy.

2. histologically confirmed invasive HER2-negative breast cancer (specific definition: HER20-1 + or HER2 2 + by immunohistochemistry but negative or no amplification by FISH or CISH, following the 2018 version of the ASCO-CAPHER2 guidelines for negative interpretation);

3. central confirmation of HRD positivity, known germline BRCA and/or systemic BRCA mutation status is allowed to be preferred.

4. age 18-70 years

5. According to RECIST 1.1, at least one measurable lesion is present;

6. ECOG score: 0-2; expected survival more than 12 weeks;

7. Previous treatment with immune checkpoint inhibitors, PARP inhibitors and HDAC inhibitors (including chidamine, romidepsin, vorinostat, benirestat, parastat, etc.);

8. All acute toxicities caused by previous anti-tumor treatment return to the level specified in the inclusion/exclusion criteria (except alopecia and other toxicities that are considered by the investigator to pose no safety risk to the subjects);

9. Female subjects of childbearing potential need to use a medically recognized contraceptive measure during the study treatment and at least 3 months after the last use of the study drug;

10. Patients with known hormone receptor status;

11. Main organ function is basically normal, and meet the following conditions:

    1. Blood routine examination criteria need to meet: HB ≥ 90 g/L (14 without blood transfusion); ANC ≥ 1.5 × 109/L; PLT ≥ 75 × 109/L;
    2. Biochemical examination need to meet the following criteria: TBIL ≤ 1.5 × ULN (upper limit of normal); ALT and AST ≤ 3 × ULN; if there is liver metastasis, ALT and AST ≤ 5 × ULN; serum Cr ≤ 1 × ULN;
    3. cardiac function: LVEF ≥ 50%

12. The subject voluntarily joined the study and signed the informed consent form.

Exclusion Criteria:

1. Uncontrolled central nervous system metastasis (defined as symptoms or requiring glucocorticoids or mannitol to control symptoms);
2. Clinically symptomatic third space effusion, pericardial effusion, pleural effusion and abdominal effusion that cannot be controlled by pumping or other treatments;
3. Currently or recently (within 30 days before enrollment) is participating in another clinical study;
4. Five Other malignant tumors (except adequately treated cervical carcinoma in situ or skin squamous cell carcinoma or controlled skin basal cell carcinoma) within the past 4 years;
5. Uncontrolled cardiac clinical symptoms or diseases, such as: (1) NYHA grade 2 or higher heart failure (2) unstable angina pectoris (3) myocardial infarction within 1 year (4) clinically significant supraventricular or ventricular arrhythmias requiring treatment or intervention (5) QTc > 470 ms;
6. Hyperactive/venous thrombotic events, such as cerebrovascular accidents (including transient ischemic attack, cerebral hemorrhage, cerebral infarction), deep venous thrombosis and pulmonary embolism;
7. He following history 24 days before signing the ICF: gastrointestinal ulcers, gastrointestinal perforation, corrosive esophagitis or gastritis, inflammatory bowel disease or inflammation, abdominal fistula, tracheoesophageal fistula or intra-abdominal abscess;
8. Factors that significantly affect oral drug absorption, such as inability to swallow, chronic diarrhea and intestinal obstruction;
9. Patients with a clear history of allergy, Potential allergy or intolerance to cidaniline, fluzoparib, and carreizumab;
10. Human immunodeficiency virus (HIV) infection, active hepatitis B (hepatitis B surface antigen positive and HBV DNA ≥ 500 IU/ml), hepatitis C (hepatitis C antibody positive and HCV-RNA above the lower limit of detection of the analytical method);
11. Female patients during pregnancy and lactation, female patients of childbearing potential with positive baseline pregnancy test or female patients of childbearing age who are unwilling to take effective contraceptive measures throughout the trial;
12. According to the investigator's judgment, the presence of concomitant diseases (including but not limited to hypertension with poor drug control, severe diabetes, neurological or psychiatric diseases, active infection, etc.) or any other condition that seriously endangers the subject's safety, may confound the study results, or affect the subject's completion of this study.