Differential Diagnosis of High-grade Neuroendocrine Neoplasms in the Digestive System

Abstract

The current World Health Organization classification of neuroendocrine neoplasms of the digestive system separates these tumors into two major categories: well-differentiated neuroendocrine tumors and poorly differentiated neuroendocrine carcinomas. These two groups are considered fundamentally different tumors, with different molecular abnormalities, prognoses, and treatment strategies. The cornerstone of the classification is proliferative rate of the tumor cells, as assessed by mitotic rate and Ki-67 labeling index. However, the range of mitotic rate and Ki-67 labeling index overlaps between high-grade, well-differentiated neuroendocrine tumor and poorly differentiated neuroendocrine carcinoma. In order to accurately separate these two entities, a systematic approach is necessary, which includes attention to the morphology, accurate assessment of the proliferative rate, review of any additional pathology materials, judicial use of immunohistochemistry, and correlation with clinical features. With this approach, the majority of tumors can be correctly classified as either high-grade, well-differentiated neuroendocrine tumor or poorly differentiated neuroendocrine carcinoma.