Pelvic Gastrointestinal Stromal Tumor (GIST) Mimicking Ovarian Cancer in a Kidney-Liver Transplant Recipient Under Chronic Immunosuppression.

Gastrointestinal stromal tumors (GISTs) are rare mesenchymal neoplasms that predominantly originate in the gastrointestinal tract. Extra-gastrointestinal GISTs can occur in atypical locations such as the pelvis, which may mimic gynecologic malignancies, creating diagnostic challenges. This case report presents a 39-year-old female with a history of Type 1 diabetes mellitus and prior kidney and liver transplantation who presented with progressive abdominal bloating and discomfort. Initial pelvic ultrasound revealed a large right adnexal mass (18.8 × 12.8 × 9.8 cm), suggestive of an ovarian mass. CT imaging confirmed a complex pelvic tumor exerting mass effect on surrounding organs, initially concerning for gynecologic malignancy. Following an unrevealing endoscopic evaluation, the patient underwent exploratory laparotomy with total abdominal hysterectomy, bilateral salpingo-oophorectomy, and tumor debulking. Intraoperative findings included a large right pelvic mass with extensive adhesions, friable tumor implants, and mesenteric lymphadenopathy. Postoperative pathology confirmed a high-grade GIST with epithelioid features, positive for DOG1 and CD117, with a Ki-67 index exceeding 30%. Molecular testing identified a KIT Exon 9 mutation, leading to initiation of imatinib therapy. Overall, this case represents an extra-GI/pelvic GIST that mimicked a primary ovarian neoplasm. We achieved a complete macroscopic cytoreduction (no gross residual disease) but explicitly note pT4 (due to intraoperative rupture), informing adjuvant KIT inhibition. This case emphasizes the diagnostic challenge of extra-GI/pelvic GISTs mimicking ovarian tumors. Studies show that GISTs mimicking primary ovarian tumors (GIST-OTs) typically occur in younger women, have lower recurrence rates (6.8% vs. 54.5% in metastatic ovarian GISTs), and achieve complete resection more frequently (> 90% vs. 57% in metastatic cases). Immunohistochemical profiling (DOG1 and CD117) and molecular testing are crucial for accurate diagnosis and treatment planning. Although imatinib remains the cornerstone of GIST management, dose adjustments based on specific mutations may be necessary, as patients with KIT Exon 9 mutations might benefit from higher dosing. Multidisciplinary approaches combining imaging, histology, and molecular profiling are essential for optimizing outcomes in these complex cases. This extra-GI/pelvic GIST occurred under chronic posttransplant immunosuppression after renal and liver transplantation; as such, we highlight the transplant-oncology interface, notably, an elevated posttransplant cancer risk, rare but documented GIST after kidney transplant, and TKI-calcineurin-inhibitor interactions that require coordinated management.