The cohorts will enroll sequentially, meaning that Cohort 1 will enroll prior to Cohort 2. Cohort 1 will evaluate exemestane's effect on the PK of entinostat. Cohort 2 will evaluate entinostat's effect on the PK of exemestane. In both Cohorts, each treatment cycle will be 28 days. Patients will participate in only one cohort.