Tucidinostat and Nab-paclitaxel in Advanced HR+/HER2- Breast Cancer

Inclusion Criteria: 1. Age≥18 years, ≤75, female; 2. Histologically confirmed HR positive and HER2 negative postmenopausal metastatic breast cancer patients \[HER2 negative is defined as immunohistochemistry(IHC) 0 or IHC 1+, and if the score of IHC is 2+, fluorescence in situ hybridization technology (FISH) test must be negative, HR positve is defined as ER or PR ≥1%\]; 3. Primary endocrine resistance or at least experienced one line of endocrine therapy for recurrent or metastatic disease; 4. No more than 1 prior line of chemothrapy for recurrent or metastatic disease; 5. Patients who have been exposed to taxanes in neoadjuvant or adjuvant setting will be allowed to enroll, if they have obtained benifits from neoadjuvant treatment or have progressed ≥ 12 months from completion of adjuvant treatment; 6. ECOG performance status ≤ 1; 7. At least one measurable disease based on RECIST v1.1 8. Adequate organ function; 9. Life expectancy is more than 3 months; 10. Willing and able to provide written informed consent. Exclusion Criteria: 1. Prior exposed to histone deacetylase inhibitors, or received taxanes for metastatic disease; 2. Known hypersensitivity to any formulation component of the study drug; 3. Received chemotherapy, targeted therapy, Chinese herbal medicine with anti-tumor indications, or immunomodulatory drugs (including thymosin, interferon, interleukin, etc.) within 4 weeks before enrollment, or still within 5 half-lives of such drugs; 4. Toxicities that did not recover to National Cancer Institute Common Adverse Event Terminology Version 5.0 (NCICTCAEv5.0) grade 0 or 1 toxicity from prior antineoplastic therapy prior to the first dose of study treatment(alopecia, grade 2 fatigue, grade 2 anemia, non-clinically critical and asymptomatic laboratory abnormalities can be enrolled); 5. Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis. 6. Pregnant or lactating female. 7. Any other conditions deemed inappropriate by the investigator to participate in this study.