Cytodiagnosis of Pancreatic Extra-Gastrointestinal Tumour Through the Hepatic Metastatic Site

Extra-gastrointestinal stromal tumours (EGIST), especially pancreatic EGIST (pEGIST), are exceedingly rare and have unknown metastatic potential. We report a cytodiagnostically challenging case of a metastatic pEGIST diagnosed from the hepatic metastatic site. A 40-year-old male presented with fever, abdominal pain and deranged liver function tests. Radiology revealed an ill-defined mass in the pancreas with multiple metastatic foci. Due to the inaccessibility of the primary lesion, fine needle aspiration cytology (FNAC) was performed on the liver lesion, which revealed a tumour with an epithelioid to spindle-cell morphology, lacking a mesenchymal matrix, causing diagnostic ambiguity between an epithelial and mesenchymal neoplasm. An extensive immunopanel on the cell block with strong CD117 and DOG1 expression confirmed a metastatic Gastrointestinal Stromal Tumour (GIST), excluding other differentials. This case underscores the utility of FNAC and immunochemistry on the cell block in diagnosing uncommon cases where only cytological samples from minimally invasive procedures are available.