Clinicopathological Spectrum and Distribution Pattern of Neuroendocrine Neoplasms of the Gastroenteropancreatic System: A Cross-sectional Study of 152 Cases

Introduction: Gastroenteropancreatic Neuroendocrine Neoplasms (GEP-NENs) are a heterogeneous group of tumours with varying biological, functional and clinical characteristics. GEPNENs develop from the diffuse neuroendocrine system of the gastroenteropancreatic tract. Aim: To analyse the clinicopathological features and the distribution pattern of GEP-NENs. Materials and Methods: In this cross-sectional observational study, all cases of primary Gastrointestinal (GI) and pancreatobiliary tract NENs diagnosed in the Department of Pathology, Regional Cancer Centre, Trivandrum, Thiruvananthapuram, Kerala, India, from 1st January 2015 to 31st December 2020 were included. Pathological features, including tumour grade and stage, were analysed. The distribution pattern of NENs in different parts of the gastroenteropancreatic tract was noted and compared with tumour grade. Results: A total of 152 patients were included in the study. The age of patients ranged from 9 to 84 years. Gastrointestinal tract involvement was noted in 124 cases and pancreatic involvement in 28 cases. The most common site in the GI tract was the duodenum (25 cases), followed by the rectum (22 cases). There were 62 resection specimens and 90 endoscopic biopsies. The Well-Differentiated Neuroendocrine Tumour (WDNET) category accounted for 124 cases, of which the most common grade was G2 74 (48.7%). Grade 3 NET comprised 7.14% of GI tract (7 cases) and 26.9% of pancreatobiliary tract WDNETs. There were 28 cases of Neuroendocrine Carcinoma (NEC), of which 13 were Small Cell Neuroendocrine Carcinoma (SCNEC) and 15 were Large Cell NEC (LCNEC). The most common site of NEC involvement was the oesophagus. On Immunohistochemical (IHC) examination, synaptophysin positivity was noted in 96% of cases and chromogranin positivity in 76.11% of cases. A pathological Tumour (pT) stage was determined in 62 resection specimens and the most common stage was pT3 29 (46.77%). Among the 18 resection specimens of NET G1 tumours, three cases showed lymph node metastasis. Of the 32 cases of resected NET G2 tumours, seven showed lymph node metastasis and five showed liver metastasis. Conclusion: Morphology and the proliferation index play a crucial role in differentiating NET from NEC. WDNETs have metastatic potential, especially to lymph nodes and the liver. The differentiation of NET G3 from NEC is important for treatment decisions.