Rectal PEComa Mimicking Gastrointestinal Stromal Tumor on Endoscopic Ultrasound.

Perivascular epithelioid cell tumors (PEComas) are rare mesenchymal neoplasms that commonly originate from the kidney, uterus, or lung, with gastrointestinal involvement being exceptionally uncommon. This case highlights the first known use of endoscopic ultrasound and endoscopic tunnel biopsy technique in diagnosing rectal PEComa. A 66-year-old woman presented with acute rectal bleeding. Imaging revealed a distal rectal mass 7.4 cm in diameter that was initially suspected to be a gastrointestinal stromal tumor. Endoscopic ultrasound with fine-needle aspiration and subsequent endoscopic tunnel biopsies confirmed the diagnosis of PEComa preoperatively. She was treated with neoadjuvant sirolimus, surgical resection, and later underwent partial hepatectomy for a solitary liver metastasis identified 3 years postoperatively. Radiologic findings in rectal PEComas often mimic gastrointestinal stromal tumor. Preoperative diagnosis is rarely achieved, but this case showed how advanced endoscopic biopsy techniques can enable early diagnosis and targeted therapy.