Retroperitoneal leiomyosarcoma mimicking gastric cancer recurrence: A case report

INTRODUCTION: Leiomyosarcoma is a rare soft tissue cancer that arises from smooth muscle cells that form involuntary muscles. Here, we report a rare case of retroperitoneal leiomyosarcoma that mimicked a metastatic tumor arising from a gastric cancer. PRESENTATION OF CASE: A 43-year-old man underwent radical total gastrectomy for gastric cancer. He underwent adjuvant chemotherapy with oral 5-fluorouracil (5-FU) for 2 years and regular follow-up. Twenty-nine months after gastrectomy, computed tomography (CT) was performed and revealed a solitary localized mass measuring 43 mm in diameter among retroperitoneal lymph nodes of the posterior inferior vena cava. This finding indicated that the previous gastric cancer recurred either in the lymph node or retroperitoneum. Second-line chemotherapy, consisting of oxaliplatin and 5-FU (FOLFOX) was administered in four cycles. However, serial CT scans showed increased tumor size. Retroperitoneal tumor did not respond to treatment, surgical resection was performed. Pathological findings led to a diagnosis of pleomorphic and epithelioid leiomyosarcoma without metastatic adenocarcinoma of the stomach. DISCUSSION: When a diagnosis of locoregional recurrence of gastric cancer in the retroperitoneum is considered, retroperitoneal leiomyosarcoma should also be considered in the differential diagnosis. CONCLUSION: Early diagnosis and concerted therapeutic efforts are important for managing misdiagnosed metastatic gastric cancer.