Study of the Effect of the Addition of SNDX-275 (Entinostat) to Continued Aromatase Inhibitor (AI) Therapy in Postmenopausal Women With ER+ Breast Cancer Whose Disease is Progressing

Exclusion Criteria

• •1. Discontinuation of AI therapy prior to study entry.
• •2. Less than 3 months treatment with most recent AI.
• •3. Rapidly progressive, life-threatening metastases, including any of the following:
• •1. Symptomatic lymphangitic metastases.
• •2. Patients with known active brain or leptomeningeal involvement.
• •4. More than one prior chemotherapy for metastatic disease.
• •5. Any chemotherapy within 3 months prior to study.
• •6. Radiotherapy to measurable lesion within 2 months prior to study.
• •7. Bisphosphonates initiated within 4 weeks prior to study start.
• •8. Allergy to benzamides or inactive components of study drug.
• •9. Previous treatment with entinostat or any other histone deacetylase (HDAC) inhibitor including valproic acid.
• •10. Patient is currently receiving treatment with any agent listed on the prohibited medication list such as valproic acid or other systemic cancer agents
• •11. Any concomitant medical condition that precludes adequate study treatment compliance or assessment, or increases patient risk in the opinion of the investigator:
• •1. Myocardial infarction or arterial thromboembolic events within 6 months, or experiencing severe or unstable angina, New York Heart Association (NYHA) Class III or IV disease and a QTc interval \>0.47 second.
• •2. Uncontrolled heart failure or hypertension, uncontrolled diabetes mellitus, uncontrolled systemic infection,
• •3. Other active malignancy within 5 years excluding basal cell carcinoma or cervical intraepithelial neoplasia \[CIN / cervical carcinoma in situ\] or melanoma in situ).
• •12. Patient currently is enrolled in (or completed within 30 days before study drug administration) another investigational drug study.