S6096 GIST of the Problem: From One Diagnosis to Another—Uncovering Jejunal Gastrointestinal Stromal Tumor (GIST) in a Young Female During Endometriosis Work-Up

Introduction: Gastrointestinal stromal tumors (GISTs) are rare mesenchymal tumors predominantly seen in older patients. Our case presents a 34-year-old woman diagnosed with a jejunal GIST during an endometriosis workup. Initially misdiagnosed due to cyclical abdominal pain & bleeding, advanced imaging prior to gynecologic surgery revealed the tumor, leading to successful intervention and ongoing treatment. Case Description/Methods: A 34-year-old woman with history of recurrent melena was hospitalized due to symptomatic anemia and low hemoglobin levels, having experienced weakness, dizziness, and black tarry stools. Her hemoglobin had dropped from 11 to 8.9 g/dL. For 3 years, she had intermittent melena, mainly during menstruation. Despite evaluations by multiple gastroenterologists, including several endoscopies and colonoscopies, no source of bleeding was found. Given the cyclic nature of her symptoms, she was referred to an endometriosis specialist. Magnetic resonance imaging (MRI) suggested deep infiltrative endometriosis but no endometrioma. During further evaluation, a computed tomography angiography (CTA) revealed a left upper quadrant jejunal mass, suspected to be a carcinoid tumor or GIST. A diagnostic laparoscopy, including removal of the mass, confirmed a jejunal GIST of spindle cell type origin. The patient is in follow-up with hematology/oncology and has started chemotherapy. Her family history includes malignancies, but genetic testing was negative for hereditary cancer syndromes. Discussion: GISTs are the most prevalent mesenchymal tumors in the gastrointestinal (GI) tract, primarily affecting individuals over the age of 50. This case illustrates a unique instance of a young woman patient presenting with symptomatic anemia. Although GISTs can cause GI bleeding, her anemia was initially misdiagnosed as endometriosis based on MRI results, delaying the identification of the jejunal mass. A subsequent computed tomography angiography successfully revealed the mass, confirmed as a jejunal GIST—an uncommon location for these tumors. GISTs arise from interstitial cells of Cajal and are frequently linked to mutations in the KIT gene or PDGFRA. Immunohistochemical staining using markers like KIT and DOG1 is crucial for diagnosis. The patient was diagnosed with a spindle cell type GIST, which constitutes about 70% of cases. The preferred treatment for non-metastatic GIST is complete surgical resection. Nonetheless, small GISTs pose a risk of malignancy, necessitating careful postoperative monitoring and possibly the use of adjuvant therapy with imatinib to minimize recurrence.