To date, empirical literature has generally been considered lacking in relation to neuroendocrine carcinomas (NECs), the highly malignant subgroup of neuroendocrine neoplasms. full text (= 164), resulting in 193 chosen articles. For inclusion, articles were to be specific for GEP-NECs or specific for GEP-NENs with relevance to GEP-NECs. Exclusion criteria were articles without relevance to GEP-NECs, articles not specific to humans, articles written in languages other than those mentioned, case studies with 5, studies, reviews published before 2010, editorials, letters, commentary, abstracts, highlights from conferences and articles specific for hereditary diseases (MEN-1  based on colorectal NECs found that when NENs were re-evaluated after the WHO 2010 classification, several NENs received a different diagnosis in relation to grading (e.g., several well-differentiated endocrine carcinomas became NECs). Also, the 2010 classification had a better prognostic value than the WHO 2000 classification. However, another study by Ozkara  found no difference in the 2004 and 2010 classifications. The 2010 WHO classification, which is widely accepted, mentions both differentiation (poor differentiation) and grade (high grade, G3) when defining GEP-NECs . However, there is controversy as to whether all high grade neoplasms are also poorly differentiated or not. Some would argue that it is possible for a well-differentiated tumour to have a Ki-67 index over 20%, whereas others would not, or find this unimportant [27,28]. A number of pathologists find the term poorly differentiated to be inadequately defined and use only the Ki-67 index for classification if the basic neuroendocrine immunochemistry is usually correct. Different nomenclature has been used to describe NECs with a non-neuroendocrine component. Several studies chose to use the term combined NEC  or composite NEC; combined when the components are topographically separated and composite when there is an intimate admixture of the two. 3.1. Small and Large Cell NECs NECs can be of small or large/intermediate cell type. Both may resemble a poorly differentiated tumour of any kind, which is why testing for cytokeratin is usually important to establish if the tumour is usually a carcinoma. Large cell NECs may show an organoid pattern with solid nests, rosette formations or acinar structures, focal necrosis and high mitotic rate. They have a low nucleus-to-cytoplasm ratio, nuclei with evident nucleoli and vesicular chromatin, and often abundant eosinophilic cytoplasm. As a rule, synaptophysin is usually diffusely positive while CgA can be frequently unfavorable. Large cell NECs often closely resemble poorly differentiated (adeno)-carcinomas, which is why testing for neuroendocrine markers is usually of great importance . Small cell NECs are indistinguishable from their counterpart buy ICA-110381 in the lung. Cells are most often small with dark nuclei of round or oval shape and scanty cytoplasm but may be slightly larger with more cytoplasm, forming solid sheets and nests. Staining for synaptophysin is usually positive in small cell NECs; however, staining for CgA can be unfavorable. According to some, neuroendocrine staining buy ICA-110381 is not obligatory for the diagnosis of small cell NECs because Rabbit Polyclonal to Cyclin C (phospho-Ser275) of their common morphology . However, small cell NECs can mimic malignant lymphoma, synovial sarcoma, PNET and other rare tumours. It is therefore wise to always perform a cytokeratin and synaptophysin staining to be certain of their diagnosis. Shia , in a study of 65 GEP-NECs, found no difference in survival between small cell and large cell NECs. However, a large study by Korse  found the five-year relative survival buy ICA-110381 to be only 6% for small cell NECs (95% confidence interval (CI) 4%C9%) in comparison to 32% in large cell NECs (95% CI 28%C37%). Shia  emphasize that there is still insufficient data on this topic, and there may be differences between small and large cell NECs in response to treatment. In the same study, Shia  found the relative frequency of small cell NECs to be higher in the oesophagus and anal canal, whereas the frequency of large cell NECs was higher in glandular mucosa-lined sites of the GI-tract. This obtaining is supported by Korse , who found a greater incidence of large cell NEC in the pancreas, as well as the large and small bowel, but a greater incidence of small cell NEC in oesophageal NECs. Also, the Nordic NEC study observed 75% and 65% of oesophageal and rectal NECs to have small cell morphology respectively while only 30% of colonic NEC had small cell morphology . Both small cell and large cell NECs can have a non-neuroendocrine component. Small.