Primary retroperitoneal mucinous cystadenocarcinoma with transition from the mesothelium

INTRODUCTION: Mucinous cystic neoplasms are uncommon among the tumors that develop in the retroperitoneum. We report a case of primary retroperitoneal mucinous cystadenocarcinoma with pathological considerations. CASE PRESENTATION: A 47‐year‐old woman complaining of abdominal discomfort presented at our hospital. Abdominal computed tomography and magnetic resonance imaging showed a large cystic tumor with small solid nodules located in the right retroperitoneum. The tumor was completely removed and the microscopic findings were consistent with primary retroperitoneal mucinous cystadenocarcinoma. Two years after the surgery, the patient is alive without recurrence of the tumor. CONCLUSION: The microscopic findings suggested that the primary retroperitoneal mucinous cystadenocarcinoma developed from the metaplasia of the remnant coelomic epithelium. A complete tumor resection that includes the adjacent peritoneum is important to prevent local recurrence.