Inclusion Criteria:  Female patients aged 18-75 years (including cutoff value); The disease condition is inoperable, recurrent breast cancer, or metastatic breast cancer; Histological or cytological confirmation of hormone receptor-positive [estrogen receptor (ER) positive and progesterone receptors (PgR) positive or negative] breast cancer; At least one measurable lesion according to RECIST 1.1; Prior treatment: have not received systemic chemotherapy for recurrent or metastatic breast cancer; Eastern Cooperative Oncology Group Performance Status of 0-1;  Adequate function of major organs meets the following requirements):  Absolute Neutrophils count≥ 1.5×10^9/L; Platelets count≥ 90×10^9/L; Hemoglobin ≥ 90g/L; Total bilirubin≤ 1.5 × the upper limit of normal (ULN); ALT and AST ≤ 2.5 × ULN; BUN and Cr ≤ 1.5 × ULN; Left ventricular ejection fraction (LVEF) ≥ 50%; QTcF(Fridericia correction) ≤ 470 ms; International normalized ratio(INR)≤1.5 × ULN; activated partial thromboplastin time(APTT) ≤ 1.5 × ULN;  Life expectancy ≥ 3 months; Have signed informed consent.  Exclusion Criteria:  Patients have untreated central nervous system (CNS) metastases; Patients with no measurable lesion according to RECIST 1.1; Patients with bilateral breast cancer; Patients with human epidermal growth factor receptor-2 (Her-2) positive; Recurrent or metastatic disease occurs within 2 years during adjuvant endocrine therapy; Patients previously received systemic chemotherapy for recurrent or metastatic breast cancer; Patients previously received any HDAC inhibitor or fulvestrant treatment; There are ascites, pleural effusion, pericardial effusion with clinical symptoms at baseline, those who need drainage, or those who have undergone drainage of serous effusion within 4 weeks before the first dose; Inability to swallow, intestinal obstruction or other factors affecting the administration and absorption of the drug; Patients with other invasive malignancies within 5 years or at the same time, with the exception of curatively-treated basal cell or squamous cell carcinoma of the skin or cervical carcinoma in situ; Patients with a history of allergies to the drug components of this regimen; Patients with active HBV and HCV infection; stable hepatitis B after drug treatment (HBV virus copy number is higher than the upper limit of reference value) and cured hepatitis C patients (HCV virus copy number exceeds the lower limit of detection method) can be included; Patients with a history of immunodeficiency, including HIV positive, or other acquired or congenital immunodeficiency disease, history of organ transplantation; Patients have uncontrolled or significant cardiovascular disease, including: Myocardial infarction (< the last 12 months); Uncontrolled angina (< the last 6 months); Congestive heart failure (< the last 6 months), or Left Ventricular Ejection Fraction (LVEF) < 50% prior to study entry; Any mental or cognitive disorder, that would interfere the ability to understand the informed consent document or the operation and compliance of study; Any other condition which is inappropriate for the study in the opinion of the investigators.