Diagnostic challenges in gastrointestinal stromal tumors: a case report of concurrent gastrointestinal stromal tumor, lymphangioma, and solid pseudopapillary neoplasm of the pancreas.

Background: Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors of the gastrointestinal tract which arise from the interstitial cells of Cajal. Nearly half of all patients present with advanced disease. GISTs can have a solid, cystic, or mixed morphology, sometimes appearing similar to other pathologies on imaging, making diagnosis of metastatic GIST difficult. Case Description: A 34-year-old woman presented with biopsy-proven GIST of the jejunum as well as a pancreatic body mass, presumed to be metastatic disease. Based on imaging and cytology, she was started on imatinib 400 mg. Surveillance imaging after 2 years of imatinib revealed regression of the jejunal GIST from 7.3 cm to 3 cm, whereas the pancreatic lesion remained stable at 4 cm. The patient ultimately underwent cytoreductive surgery which revealed several individual large cystic masses, a distinct pancreatic mid-body lesion, and proximal jejunal GIST. Final pathology of the cystic masses returned as lymphangiomas, while the pancreatic resection revealed a solid pseudopapillary neoplasm. Pathology of the jejunal mass was consistent with GIST. Next-generation sequencing showed an exon 11 Conclusions: This case report highlights the importance of considering secondary malignancies when faced with an initial diagnosis of metastatic GIST and the diagnostic challenges of cystic lesions. The patient demonstrated imatinib treatment response in her small bowel lesion, yet no change in the pancreatic lesion nor cystic masses associated with the stomach. Additionally, GISTs rarely metastasize to the pancreas, with only a handful of cases reported in the literature; this further emphasizes the need to consider alternative or additional diagnoses when patients without predisposing factors to multifocal GIST present with multiple lesions, even at younger ages.