Rectal Gastrointestinal Stromal Tumor Complicated by Tumor Lysis Syndrome after Imatinib Initiation: A Rare and Fatal Case.

Introduction: Gastrointestinal stromal tumors (GISTs) are rare mesenchymal connective tumors. They generally develop from the gastric or intestinal wallor. Rectal location is rare. In fact, rectal GISTs account for 5% of cases and 0.1% of all rectal tumors. Case Presentation: We report the case of a stromal tumor of rectal localization in order to study the clinical, anatomopathological and radiological particularities of this entity. We report the case of a 73-year-old patient who was initially admitted for a stent placement. A rectoscopy showed a half circumferential rectal process. It was situated at 2 cm from the anal verge. The magnetic resonance imaging of the pelvis showed a large tumor of the lower rectum, with a focal rupture of the right rectal wall and invading the sphincter apparatus. Pathological examination revealed a proliferation of spindle-shaped cells with abundant cytoplasm and ovoid atypical nuclei with a high mitotic index. The immunohistochemical study showed that the tumor cells were positive for CKit and DOG1 and negative for AML and PS100. The retained diagnosis was high-risk spindle cell GIST. Conclusion: Rectal GISTs are rare tumors. Diagnosis is based on anatomopathological examination with immunohistochemical study. Surgical resection is the standard treatment for localized GIST. Imatinib is the first-line prescribed treatment, with particular attention to potentially life-threatening adverse effects.