A Rare Case of a Vaginal Solitary Fibrous Tumor, Presenting as a Cystic Mass, Showing NAB2ex4-STAT6ex2 Fusion and STAT6 Immunostaining

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Solitary fibrous tumor (SFT) has been rarely documented in the female genital tract. Until now, only 5 such cases have been reported in the vagina. A 40-yr-old referred to us with a history of antitubercular treatment and intra-abdominal adhesions; for which she previously underwent laparoscopic. Subsequently, she developed a vaginal mass, which appeared as a complex cyst on ultrasonogram. Histopathologic examination of the excised mass revealed a cellular spindle cell tumor with collagenous deposition in the stroma. The tumor cells were composed of oval to spindle shaped nuclei and were arranged in a diffuse, as well as in a focally, hemangiopercytomatous pattern. There were no significant mitotic figures or tumor necrosis. By immunohistochemistry, the tumor cells showed patchy positivity for CD34 and diffuse intranuclear positivity for STAT6, along with cytoplasmic positivity for MIC2 and BCL2. Few cells were estrogen receptor positive. MIB1/Ki67 highlighted 2% to 3% tumor nuclei (low). Diagnosis of a SFT was rendered. Subsequently, the tumor was subjected to molecular analysis, by reverse transcriptase-polymerase chain reaction and sequencing, which revealed presence of NAB2ex4-STAT6ex2 fusion transcript. This case constitutes the first case of a vaginal SFT confirmed by STAT6 immunostaining and NAB2-STAT6 fusion. It exemplifies the role of specific immunohistochemical markers, such as STAT6 in differentiating a SFT from various other spindle cell tumors occurring in this location. Literature review of similar reported cases and treatment implications in such cases are discussed.

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