Retroperitoneal Fat-Forming Solitary Fibrous Tumor in a Gynecological Patient: A Case Report and Literature Review

Background: Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm that can occur in a wide range of anatomical locations. Fat-forming SFT is a rare morphological variant of SFT characterized by an additional adipocyte component and a clinical course ranging from benign to overtly malignant. Case: We report the case of a 65-year-old gynecologic patient presenting with a large mass in the left adnexal region, which was found during surgery to originate from the retroperitoneal area. Histological and immunohistochemical (IHC) analyses revealed dense spindle cells that were positive for cluster of differentiation 34 (CD34), cluster of differentiation 99 (CD99), B-cell lymphoma 2 (BCL-2), and signal transducer and activator of transcription 6 (STAT6). Together with the presence of S-100-positive adipocytes within the tumor, the IHC results confirmed the diagnosis of fat-forming SFT. The patient showed no signs of recurrence or metastasis 24 months after surgery, and lifelong follow-up was planned. Conclusion: Although fat-forming SFT is very rare in gynecology, this diagnosis should be considered whenever a large pelvic or retroperitoneal mass is identified prior to surgical intervention.