Gastric cancer and pleomorphic liposarcoma: A Case Report of synchronous dual primary malignancies.

A 62-year-old male presented with a 9-month history of intermittent epigastric distension and pain, accompanied by acid reflux, nausea, vomiting, melena, and weight loss. Physical examination revealed epigastric tenderness. Laboratory tests showed hemoglobin of 94.0 g/L and serum albumin of 22.55 g/L. Gastroscopy identified gastric cancer in the antrum with gastric retention. Pathological biopsy of the antrum confirmed poorly differentiated adenocarcinoma. Colonoscopy revealed multiple small colonic polyps (maximum diameter 5 mm). Contrast-enhanced computed tomography (CT) of the upper abdomen demonstrated an approximately 6 cm lesion in the gastric antrum and a mesenchymal malignant tumor measuring approximately 10 cm in diameter in the left hepatorenal space, along with ascites in the abdominal and pelvic cavities. The patient received preoperative nutritional support, which improved his anemia, hypoalbuminemia, and overall physical condition. Under general anesthesia, he underwent distal gastrectomy with D2 lymph node dissection and Billroth II reconstruction, combined with resection of the retroperitoneal tumor. Postoperative pathology confirmed the gastric lesion as an ulcerative poorly differentiated adenocarcinoma and the retroperitoneal tumor as a pleomorphic liposarcoma (PLPS). The patient recovered well and was discharged. For the gastric cancer, he received 6 cycles of adjuvant chemotherapy with the SOX regimen (Oxaliplatin plus S-1). Follow-up examinations, including gastroscopy and contrast-enhanced CT of the upper abdomen, were performed at 3, 6, 12, 18, 24, 30, 36, 42, and 48 months postoperatively. No evidence of tumor recurrence was detected during this follow-up period. This paper reports a concurrent case of gastric cancer and PLPS, detailing the case characteristics, diagnostic and therapeutic procedures, and postoperative follow-up. The purpose of this study is to analyze the features of this Multiple primary malignant neoplasms (MPMN) case and provide a reference for selecting appropriate clinical treatments to improve patient prognosis.