Aberrant HepPar 1 Expression in Well-Differentiated Neuroendocrine Tumors Metastasized to the Liver: Clinicopathologic Study of 75 Tumors

Background Neuroendocrine tumors frequently metastasize to the liver. The histologic features of eosinophilic cytoplasm with a trabecular growth pattern surrounded by a capillary network mimic those of hepatocellular carcinoma. No previous studies have extensively investigated aberrant HepPar 1 expression in well-differentiated neuroendocrine tumors metastasized to the liver. Design We identified 75 tumors of well-differentiated neuroendocrine tumors metastasized to the liver from January 2020 to June 2023 and collected clinicopathologic data, including age, sex, and pathologic diagnosis. Twenty-six specimens were biopsy samples, and forty-nine were surgical specimens. A representative block was chosen for immunohistochemistry. Aberrant expression of HepPar 1 in metastatic well-differentiated neuroendocrine tumors was examined immunohistochemically. Results The 75 patients comprised 37 men and 38 women ranging in age from 21 to 87 years (mean: 61.5 years). Thirty-eight tumors were grade 1, 27 were grade 2, and 10 were grade 3. Only 1 grade 3 tumor (1%) showed diffuse aberrant HepPar 1 expression; 8 tumors (5 grade 2 and 3 grade 3) (11%) showed rare aberrant expression; and the remaining 66 tumors (88%) were completely negative. Aberrant HepPar 1 staining was significantly associated with higher tumor grade ( P < .05). Conclusion Aberrant HepPar 1 expression in well-differentiated neuroendocrine tumors metastasized to the liver is extremely rare. HepPar 1 can be reliably used to differentiate neuroendocrine tumors from hepatocellular carcinomas, with some caveats.