Gastrointestinal: A case of pancreatic gastrointestinal stromal tumor diagnosed by endoscopic ultrasound fine needle biopsy

A 67-year-old female underwent pancreatic head-sparing duodenectomy for a duodenal submucosal tumor that was diagnosed as a gastrointestinal stromal tumor (GIST). After surgery, she was treated with imatinib for 3 years. Five years after diagnosis, contrast-enhanced computed tomography revealed an 11-mm, hypervascularized, neoplastic lesion in the pancreatic head of this patient (Fig. 1a). Abdominal ultrasonography (AUS) showed a well-defined, smooth, internally hypoechoic mass in the pancreatic head. Contrast-enhanced AUS showed the same lesion as being hypervascularized, with slightly earlier contrasting in the mass than the surrounding pancreas (Fig. 1b). Endoscopic ultrasonography (EUS) revealed a borderline-clear hypoechoic lesion. EUS-guided fine needle biopsies of this lesion revealed the presence of spindle cells in this mass by rapid, on-site cytologic evaluation (Fig. 2a). Hematoxylin–eosin staining and immunostaining revealed that these spindle cells (Fig. 2b) were positive for KIT and CD34 (Fig. 2c,d), leading to the diagnosis of GIST in the pancreas. Retrospective review of the preoperative computed tomography 5 years earlier revealed a 6 mm, slowly progressing lesion in the pancreatic head. Currently, this small GIST lesion in the pancreas is under careful observation with surgical resection being considered in case of future growth. GISTs arising from the pancreas are broadly classified into pancreatic primary extra-gastrointestinal stromal tumor (EGISTs) and metastatic GISTs. Primary pancreatic EGISTs are rare, accounting for ~5% of all EGISTs cases. Similar to EGISTs, metastatic GISTs occur very infrequently. To distinguish between the two, it is necessary to search for mutations of the KIT gene in the collected tumor cells. However, this case could not be carried out in this case due to the small volume of the fine needle biopsy specimen. Although this case was a small lesion and required differentiation from a neuroendocrine tumor and other pancreatic hypervascularized tumors on clinical imaging, EUS was useful and able to accurately diagnose the GIST in the pancreas, an uncommon disease.