Primary Hepatic Extra-gastrointestinal Stromal Tumors: Molecular Pathogenesis, Immunohistopathology, and Treatment

Gastrointestinal stromal tumors are the most common mesenchymal tumors of the gastrointestinal tract. They originate from the interstitial cells of Cajal and are usually found in extrahepatic gastrointestinal sites. However, a small subset are derived from the liver and are known as primary hepatic gastrointestinal stromal tumors (PHGIST). They have a poor prognosis and are historically difficult to diagnose. Our objective was to review and update the latest evidence-based knowledge concerning PHGIST, with a focus on epidemiology, etiology, pathophysiology, clinical presentation, histopathology, and treatment. These tumors are usually found incidentally, occur sporadically, and are associated with mutations of KIT and PDGFRA genes. PHGIST is a diagnosis of exclusion, as it has the same molecular, immunochemistry and histological appearance as gastrointestinal stromal tumors (GIST). Thus, imaging, such as positron emission tomography-computed tomography (PET-CT) must be used to rule out metastatic GIST before a diagnosis can be made. However, with mutation analysis and pharmacological advances, tyrosine kinase inhibitors are typically pursued with or without surgical intervention. Other potential treatments include transcatheter arterial chemoembolization and tumor ablation. However, these are typically considered palliative options. As there are only a limited number of publications regarding PHGIST, data concerning morbidity and mortality are not yet available. Immunohistopathology can help develop screening guidelines and evaluating resistance to treatment.