Large Pancreatic Gastrointestinal Stromal Tumor: A Diagnostic Quandary.

Gastrointestinal stromal tumors (GISTs) are rare mesenchymal neoplasms typically arising from the gastrointestinal tract, most often in the stomach or small intestine. Primary pancreatic GIST is exceedingly rare, with fewer than 50 cases reported in the literature. We present a unique case of a 77-year-old female who was found to have a 6.5 cm complex mass in the left abdomen with inconclusive imaging findings. Endoscopic ultrasound (EUS) further characterized the lesion as a mixed solid and cystic mass with peripheral enhancement, but its origin remained uncertain. Pathology revealed a spindle cell type GIST. Given the diagnostic ambiguity, the patient underwent diagnostic laparoscopy, which definitively identified the mass as originating from the pancreatic tail, confirming the rare diagnosis of primary pancreatic GIST. Despite recommendations for surgical resection or treatment with imatinib, the patient declined both and chose to pursue close surveillance. The patient's clinical condition remained stable one year after initial diagnosis. This case underscores the importance of including pancreatic GIST in the differential diagnosis of atypical pancreatic masses, especially those with mixed solid and cystic components. It also highlights the role of EUS as well as laparoscopy in resolving diagnostic uncertainty for complex abdominal masses. Further studies are needed to better understand the natural history and optimal management of low-risk, asymptomatic pancreatic GISTs. This case also highlights the importance of shared decision-making in the management of conditions where guidelines are not well-developed.