Tumor stage is also fundamental information, which never should be missing in the pathology report of abdominal neuroendocrine tumors, because it complements the prognostic information and the clinical handling of these patients. The assessment schemes on neuroendocrine tumor extent are anatomical site-specific for the definition of tumor (T) parameters based on size and invasion because of the significant differences in clinical behavior of these tumors according to the organs of origin. By contrast, for the nodal (N) and distant metastasis (M) definition, current clinical experience and biological knowledge about neuroendocrine neoplasms is insufficient for further subdividing them, beyond a mere dichotomous separation based on the occurrence or absence of tumor deposits. The current staging systems of abdominal neuroendocrine neoplasms are in keeping with the 8^th edition of the UICC and AJCC classification for the single organs (stomach, duodenum/ampulla/proximal jejunum, pancreas, lower jejunum and ileum, appendix, large bowel and rectum). The ENETS staging system overlaps largely with these proposals, with some differences and conflicting results in the prognostic stratification of neoplasms arising in the stomach, pancreas and appendix [26, 27]. In cases of discrepancy, both staging classifications should be mentioned and the worst stage used for classification [35]. For example, the ENETS staging system of pancreatic NEN is better suited than the UICC and AJCC proposal to forecasting patient survival, while the opposite holds true for appendix NEN. Lastly, in the stomach, both the TNM/AJCC and ENETS systems predict survival especially in NEC, while the TNM/AJCC seems to be superior in the NET subgroups [51]. An integration of staging and grading (the so-called TGM system) has been proposed in keeping with other malignancies as a tool for better predicting survival in pancreatic NEN as compared with singly used stage and grade schemes [52], but further confirmation is still needed before accepting this innovative approach into the clinical practice of abdominal neuroendocrine neoplasms.

Pathology reports of abdominal neuroendocrine tumors should always contain information useful for the best clinical handling of patients. In particular, anatomical location, appropriate classification (tumor vs. carcinoma), differentiation levels (well vs. poor differentiated), 2010 WHO/ENETS tumor grading (G1 to G3) with details on mitotic count and Ki-67 LI, and the TNM/AJCC/ENETS pathological stage should not be missing in any diagnosis of abdominal neuroendocrine neoplasms, especially resection specimens. Small biopsy samples in turn are most often the only available material in the setting of metastatic NEN, where grading assessment is clinically warranted. The time-honored and conceptually surpassed term “carcinoid” should be avoided, and only confined to carcinoid syndrome-associated NET. On surgical specimens, additional histologic features such as microscopic multicentric disease, presence and extent of non-ischemic necrosis, vascular and perineural invasion, definition of resection margins and evaluation of the functional status may help better complement the overall clinical assessment. Upon request or inside specific trials, information about predictive markers, such as somatostatin receptors, m-TOR pathway molecules or thymidylate synthase expression, may be integrated into the pathology reports to best manage these patients on clinical grounds. All pathology diagnoses should be discussed within multidisciplinary teams.