Tumor size and perineural invasion predict outcome of gastric high grade neuroendocrine neoplasms.

A new subcategory, grade 3 neuroendocrine tumors, is incorporated into the grading system of pancreatic neuroendocrine neoplasms in the 2017 WHO classification in order to differentiate grade 3 neuroendocrine tumors from neuroendocrine carcinomas. The 2019 WHO classification extends the concept of grade 3 neuroendocrine tumors to gastrointestinal high grade neuroendocrine neoplasms. However, there is still limited study focusing on the gastric grade 3 neuroendocrine tumors and gastric neuroendocrine carcinomas. We retrospectively enrolled 151 gastric high grade neuroendocrine neoplasms patients, who underwent radical resection from January 2007 to December 2015. Clinicopathologic and prognostic features were studied. The Surveillance, Epidemiology, and End Results database was used to verify the prognostic determinants found in Zhongshan cohort. Neuroendocrine carcinomas showed higher Ki67 index and higher mitotic count than grade 3 neuroendocrine tumors. We identified 109 (72.2%) patients of neuroendocrine carcinomas, 12 (7.9%) patients of grade 3 neuroendocrine tumors and 30 (19.9%) patients of mixed neuroendocrine non-neuroendocrine neoplasms. Although neuroendocrine carcinomas demonstrated higher Ki67 index (p=0.004) and mitoses (p=0.001) than grade 3 neuroendocrine tumors, their prognosis after radical resection did not demonstrate significant differences (p=0.709). Tumor size, perineural invasion and TNM stage were independent prognostic factors of gastric high grade neuroendocrine neoplasms.