Uterine leiomyoma mimicking a gastrointestinal stromal tumor: a diagnostic pitfall of CD117 positivity - case report and review of the literature.

BACKGROUND: Uterine leiomyomas are the most common benign tumors of the female genital tract. They are usually easily recognized based on clinical and imaging findings. However, in rare cases, atypical presentations can mimic intra-abdominal mesenchymal tumors such as gastrointestinal stromal tumors (GISTs), leading to potential diagnostic confusion. Immunohistochemical overlap, particularly focal CD117 (c-Kit) expression in smooth-muscle tumors, can further complicate the distinction between these entities. CASE PRESENTATION: We report the case of a 37-year-old woman presenting with progressive abdominal distension over two years. Imaging revealed a large, well-circumscribed abdominopelvic mass centered on the mesentery, initially suggestive of a mesenchymal tumor. A CT-guided biopsy showed a spindle-cell proliferation with focal CD117 positivity, leading to a preliminary diagnosis of GIST. During surgery, a markedly enlarged polymyomatous uterus was discovered. Myomectomy of five large fibroids was performed, and histopathological examination confirmed benign leiomyomas expressing CD117 focally but negative for DOG-1 and CD34. The postoperative course was uneventful. CONCLUSION: This case highlights a rare but significant diagnostic pitfall: uterine leiomyomas may present as abdominopelvic masses mimicking GISTs both radiologically and immunohistochemically. Awareness of this overlap and comprehensive immunohistochemical evaluation are essential to avoid misdiagnosis and inappropriate management.