Phase I (Stage Ib). To evaluate the safety and tolerability of chidamide in combination with abemaciclib and fulvestrant in locally advanced/metastatic HR+/HER2- breast cancer and to determine the recommended phase II dose of this combination regimen.~Stage 2 (Phase II). To determine the efficacy and safety of chidamide in combination with abemaciclib and fulvestrant in locally advanced/metastatic HR+/HER2- breast cancer with the recommended phase II dose.
To evaluate the efficacy and safety of chidamide in combination with abemaciclib and fulvestrant in locally advanced/metastatic HR+/HER2- breast cancer who had failed prior palbociclib therapy