|Neuroendocrine tumors are also referred to as neoplasms; these are abnormal growth of tissues that arise from endocrine (hormonal) cells and nervous systems. Many are harmless in the long run (benign), while some become progressively worse (malignant). These neuroendocrine tumors are often called carcinoid tumors which most commonly occur in the intestine. Review articles are the summary of current state of understanding on a particular research topic. They analyse or discuss research previously published by scientist and academicians rather than reporting novel research results. Review article comes in the form of systematic reviews and literature reviews and are a form of secondary literature. Systematic reviews determine an objective list of criteria, and find all previously published original research papers that meet the criteria. They then compare the results presented in these papers. Literature reviews, by contrast, provide a summary of what the authors believe are the best and most relevant prior publications. The concept of "review article" is separate from the concept of peer-reviewed literature. It is possible for a review to be peer-reviewed, and it is possible for a review to be non-peer-reviewed.