Pelvic Retroperitoneal Solitary Fibrous Tumor: Two Cases Including Doege-Potter Syndrome.

Solitary fibrous tumor (SFT) is a rare mesenchymal lesion that typically exhibits no aggressive behavior and has low metastatic potential. While it is commonly described in the pleura and thorax, its occurrence in the retroperitoneal pelvic cavity is uncommon. We report two cases of pelvic retroperitoneal SFT treated at the Instituto Nacional de Cancerología in Colombia. The first case involved a 76-year-old man with a pelvic mass that developed over one year. Computed tomography (CT) showed a retroperitoneal tumor near the prostate and a suspicious pulmonary nodule. Biopsy confirmed high-risk SFT with signal transducer and activator of transcription 6 (STAT6) positivity and a Ki-67 index of 40%. The patient underwent extensive surgical resection with clear margins, during which an incidental prostatic adenocarcinoma was identified. At 12 months of follow-up, no evidence of recurrence was observed. The second case involved a 35-year-old man with severe hypoglycemia due to Doege-Potter syndrome secondary to pelvic SFT. Imaging demonstrated a large pelvic retroperitoneal mass causing obstructive uropathy, requiring bilateral nephrostomies. Biopsy confirmed high-risk SFT with STAT6 positivity and a Ki-67 index of 40%. The patient underwent extensive surgical resection complicated by massive intraoperative bleeding, requiring a two-stage procedure. Pathology revealed margins in contact; however, the postoperative course was favorable. At six months of follow-up, the patient remained free of hypoglycemic episodes and without radiological progression. SFT remains a rare condition, especially when located in the retroperitoneal pelvic region. Both cases highlight the clinicopathological variability of the disease and emphasize that early diagnostic suspicion and multidisciplinary management are crucial to optimizing treatment outcomes.