Abexinostat, Palbociclib, and Fulvestrant for the Treatment of Breast or Gynecologic Cancer

Inclusion Criteria: * BREAST CANCER: Participants must have histologically confirmed hormone receptor (HR)+, HER2- locally advanced or metastatic stage IV breast cancer. HER2- should be defined as 0 or 1 by immunohistochemistry, or HER2 gene amplification by fluorescence in situ hybridization (FISH), chromogenic in situ hybridization (CISH), or in situ hybridization (ISH) performed upon the primary tumor or metastatic lesion (ration \< 2 and HER2 copy \< 4). Estrogen receptor (ER) and progesterone receptor (PR) expression positivity is defined as more than 5% of tumor cells nuclei positive by immunohistochemistry in the sample on testing * BREAST CANCER: Patients must have had disease progression after treatment with anti-estrogen therapy combined with Cyclin-dependent kinase 4/6 (CDK4/6) inhibitor after a minimum of at least 3 months therapy in the metastatic setting and no more than 3 prior lines of systemic therapy for metastatic breast cancer (MBC), unrestricted prior therapy in the dose escalation * Note: Patients with breast cancer who were not previously treated with CDK4/6 inhibitors or have not tolerated full doses of prior ribociclib or palbociclib or abemaciclib are not eligible * ENDOMETRIAL CANCER: Patients must have histologically confirmed metastatic endometrial cancer of endometrioid type * ENDOMETRIAL CANCER: Tumors must have ER expression * ENDOMETRIAL CANCER: Patients must have received a maximum of one line of hormonal therapy for the treatment of endo…