Extragastrointestinal stromal tumor presenting as a recurrent vulvar mass

Extragastrointestinal stromal tumors (EGIST) primarily arising from the female genital tract are extremely rare. We report a case of EGIST presenting as a recurrent vulvar mass with genetic analyses. A 59-year-old woman was found to have a 4-cm recurrent mass in the right vulva after 6 months of the first resection. Histological findings showed that the uniform spindle cells formed interlacing bundles, with high cellular density and mild to moderate atypia. Mitotic activity averaged 10 mitoses per 50 high-power fields. Immunohistochemical evaluation revealed that the tumor cells exhibited strong and diffuse staining for CD117, CD34 and DOG1. Ki67 labeling was approximately 15%. Molecular analysis showed an in-frame protein deletion (P551_Q556del) at exon 11 of c-KIT. The tumor was diagnosed as an EGIST. The patient was treated with imatinib, and was healthy at 12-month follow-up. EGIST should be considered in the differential diagnosis of vulvar mesenchymal tumors.