Report of a case: Retroperitoneal mucinous cystadenocarcinoma with rapid progression

INTRODUCTION: Retroperitoneal mucinous cystic neoplasms are uncommon, and little is known about the etiology of the disease. Malignant forms of these are extremely rare. Here, we report a case of primary retroperitoneal mucinous cystadenocarcinoma (PRMC), which demonstrated unexpectedly aggressive progression despite finding only a limited area of adenocarcinoma. PRESENTATION OF CASE: A 62-year-old woman with a complaint of abdominal discomfort was admitted to the hospital. Abdominal CT and MRI showed multiple large retroperitoneal cysts dislocating the right kidney nearly to the center of the abdomen. Transabdominal resection of the cysts was performed. Those cysts contained 1100 ml of mucinous fluids in total. Cytological examination of those fluids revealed no malignant cells. The cyst wall was lined with mucinous epithelial cells, and contained some ovarian-type stroma. Also, there was a focal area of adenocarcinoma in the cyst wall, and the lesion was diagnosed as primary retroperitoneal mucinous cystadenocarcinoma. Eight months later, the patient developed lumbar bone metastasis. Chemotherapy with S-1, an oral fluoropyrimidine, and docetaxel had been begun immediately; however, the disease had rapidly spread in the retroperitoneum. Eventually, the patient died of the disease 15 months after surgery. DISCUSSION: Retroperitoneal mucinous cystic neoplasms are considered to be metaplasia of embryonal coelomic epithelium. Complete excision without rupture is essential. However, variance of biological aggressiveness might exist in PRMCs. CONCLUSION: Retroperitoneal mucinous cystadenocarcinoma is a rare tumor, and it is urgently necessary to elucidate the etiology of an effective therapy for the disease.