Additional Study Information: You are being asked to participate in this study because you have a neuroendocrine tumor that has spread to your organs. You may or may not have had prior treatment for your neuroendocrine tumor. The purpose of this study is to determine if a drug called entinostat has efficacy in shrinking neuroendocrine tumors. People who usually have metastatic neuroendocrine tumors may be treated with octreotide or lanreotide and also with everolimus. There are other ongoing clinical trials with different agents for patients with your kind of disease. Approximately 40 individuals will be asked to participate in this study.