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There is an increased risk of second primary cancers (SPCs) after neuroendocrine tumor (NET) diagnosis. The clinical significance of SPCs in this population is unknown. The purpose of this study was to evaluate the association between SPCs after NET diagnosis and survival. We performed a population-based, retrospective cohort study of NET patients (gastrointestinal, pancreatic, or lung primary) from 2000 to 2016 using the Surveillance, Epidemiology, and End Results database. Cox regression models assessed the association between SPCs and NET-specific (NET-SS), cancer-specific (CSS), and overall survival (OS). Of 58,553 NET patients, 7.9% experienced an SPC. SPCs were associated with worse OS (hazard ratio (HR) 2.14, 95% CI 1.94-2.36) and CSS (HR 2.31, 95% CI 2.06-2.59) with no difference in NET-SS (HR 1.04, 95% CI 0.87-1.23). Stratified analyses by histologic grade showed similar results for well and moderately differentiated NETs, but no difference in OS or CSS for poorly differentiated NETs (P > 0.05). In stratified analyses by NET site, SPCs were associated with worse OS (HR 3.41, 95% CI 3.01-3.87) and CSS (HR 4.96, 95% CI 4.28-5.74) in gastrointestinal NETs and worse OS (HR 1.25, 95% CI 1.03-1.52) with no difference in CSS (HR 1.08, 95% CI 0.85-1.36) in lung NETs. SPCs were not associated with a difference in OS or CSS in pancreatic NETs (P > 0.05). In conclusion, SPCs after NETs were associated with inferior OS and CSS compared to no SPC but were not associated with NET-SS. These data highlight the need for long-term follow-up in NETs to include the detection of SPCs to ensure early diagnosis and timely management. [ABSTRACT FROM AUTHOR]

High-grade neuroendocrine neoplasms are a rare disease entity and account for approximately 10% of all neuroendocrine neoplasms. Because of their rarity, there is an overall lack of prospectively collected data available to advise practitioners as to how best to manage these patients. As a result, best practices are largely based on expert opinion. Recently, a distinction was made between well-differentiated high-grade (G3) neuroendocrine tumors and poorly differentiated neuroendocrine carcinomas, and with this, pathologic details, appropriate imaging practices and treatment have become more complex. In an effort to provide practitioners with the best gui dance for the management of patients with high-grade neuroendocrine neoplasms of the gastrointestinal tract, pancreas, and gynecologic system, the North American Neuroendocrine Tumor Society convened a panel of experts to develop a set of recommendations and a treatment algorithm that may be used by practitioners for the care of these patients. Here, we provide consensus recommendations from the panel on pathology, imaging practices, management of localized disease, management of metastatic disease and surveillance and draw key distinctions as to the approach that should be utilized in patients with well-differentiated G3 neuroendocrine tumors vs poorly differentiated neuroendocrine carcinomas. [ABSTRACT FROM AUTHOR]