Extragastrointestinal stromal tumors presenting as vulvovaginal/rectovaginal septal masses: a diagnostic pitfall

Gastrointestinal stromal tumor (GIST) are the most common mesenchymal tumors of the gastrointestinal (GI) tract. Most GISTs arise in the stomach and small bowel, whereas a small number occur elsewhere in the GI tract. Rare cases are identified outside the GI tract and are collectively known as extragastrointestinal stromal tumors (EGISTs). Because of their malignant potential and recent advances in the management of GISTs with imatinib mesylate (Gleevec, Glivec), it is imperative that these tumors are correctly diagnosed. In this study, we reviewed the clinical and pathologic characteristics of 3 cases of EGIST presenting as vulvovaginal/rectovaginal septal masses that were originally misdiagnosed, presumably due to their unusual anatomic locations. The original diagnoses were leiomyoma in one case and leiomyosarcoma in 2 cases. The lesions were localized to the rectovaginal septum () or vagina () and ranged from 4 to 8 cm in diameter. All 3 lesions had a spindle cell morphology that mimicked a smooth muscle tumor. Mitotic figures numbered from 12/50 to 16/50 high power fields (HPFs; median 15). Immunohistochemistry revealed that all 3 cases were strongly positive for KIT (CD117) and CD34 and negative for smooth muscle actin, desmin, pan-cytokeratin, and estrogen receptor. KIT sequence analysis revealed oncogenic mutations in all 3 cases. The first tumor recurred at 2 years and the second tumor recurred at 10 years; the third case is too recent for meaningful follow-up. EGISTs that present as gynecologic masses are rare but may be more common than is currently recognized. Misdiagnosis may lead to inappropriate therapy because conventional chemotherapy and radiotherapy are not effective in the treatment of GISTs, whereas imatinib mesylate (Gleevec, Glivec) has a proven role in managing these tumors. Thus, it is imperative to consider EGISTs in the differential diagnosis of mesenchymal neoplasms in the vulvovaginal/rectovaginal septum.