Jérôme Cros

Isolated hepatic localizations of neuroendocrine tumors (NETs) are generally considered as metastatic NETs of unknown primary but could correspond to primary hepatic NETs (PHNETs), a poorly explored entity. We aimed to describe the clinicopathological and molecular features of PHNETs and compare them with other primary NETs. We assembled a retrospective cohort of patients managed for hepatic localization of NET without extra‐hepatic primary tumor after exhaustive clinical, imaging, and immunohistochemical characterization. We performed whole‐exome sequencing with mutational and copy number analysis. Transcriptomic profiles were compared with pancreatic ( n = 31), small‐bowel ( n = 22), and lung ( n = 15) NETs using principal component analysis, unsupervised clustering, and gene set enrichment analysis. Among 27 screened patients, 16 had PHNET (solitary tumor in 63%, median size 11 cm, G2 NETs in 81%) following clinical and pathological review. DNA analyses showed ‘foregut‐like’ genomic profiles with frequent alterations in pathways of Fanconi DNA repair (75%), histone modifiers (58%), adherens junctions (58%), and cell cycle control (50%). The most frequently involved genes were KMT2A (58%), ATM (42%), CDH1 , CDKN2C , FANCF , and MEN1 (33% each). Transcriptomic analyses showed that PHNETs clustered closer to foregut (pancreatic, lung) NETs than to midgut (small‐bowel) NETs, while remaining a distinct entity with a specific profile. Assessment of potentially predictive biomarkers suggested efficacy of treatments usually active in foregut NETs. In conclusion, PHNETs display a foregut‐like molecular profile distinct from other types of NETs, with recurrent molecular alterations. Upon exhaustive work‐up to exclude an unrecognized primary tumor, PHNETs should not be considered metastatic NETs from an unknown primary. © 2022 The Pathological Society of Great Britain and Ireland.