Surgical Resection of Undifferentiated Pleomorphic Sarcoma (UPS) With Jejunal Perforation, A Suspected Case of Metastasis of Lung Cancer: A Case Report

Background: Undifferentiated pleomorphic sarcoma (UPS) in the gastrointestinal tract is rare. According to the diagnostic criteria after the World Health Organization 2013 reclassification, there has been only one case of UPS with perforation of the gastrointestinal tract.Case presentation: A 71-year-old man who was undergoing outpatient chemotherapy at the department of respiratory medicine of our hospital for lung cancer and brain metastasis, was admitted to our hospital with sudden high fever and abdominal pain. A computed tomography scan showed free air in the abdominal cavity with thickening of part of the jejunal wall. We suspected jejunal metastasis of lung cancer and performed emergency surgery for acute peritonitis due to gastrointestinal perforation in the same area. A Bormann type 2 tumor was found in the jejunum with perforation. The histopathological diagnosis was UPS. Ten months have passed since the surgery, and there has been no recurrence of UPS and no significant change in lung cancer.Conclusions: Primary UPS of the gastrointestinal tract is rare, and cases with perforation are extremely rare. Currently, ten months have passed since the surgery, and no recurrence has been observed. We encountered a case of UPS in which it was difficult to distinguish metastasis from lung cancer to the jejunum, and emergency surgery gave us the chance to confirm the definitive diagnosis and save the patient's life.