Retroperitoneal smooth muscle tumor of uncertain malignant potential after hysterectomy: a case report.

Introduction: Smooth muscle tumors of uncertain malignant potential represent a histologically heterogeneous group of uterine smooth muscle tumors that cannot be diagnosed as either benign or malignant. Smooth muscle tumors of uncertain malignant potential are usually clinically benign, but should be considered tumors of low malignant potential because they can occasionally recur or metastasize to distant sites.

Case Presentation: We report the case of a 62-year-old Mongol woman diagnosed with a retroperitoneal smooth muscle tumor of uncertain malignant potential and lung metastasis, with a history of prior hysterectomy. The case was initially misdiagnosed as retroperitoneal sarcoma, and our patient received chemotherapy. However, no interval change in the size of the retroperitoneal mass and metastatic lung nodules was seen over a period of at least five years. She underwent partial resection of the retroperitoneal mass for the purposes of debulking and establishing a histopathological diagnosis. The diagnosis of the retroperitoneal mass was then confirmed as a smooth muscle tumor of uncertain malignant potential.

Conclusion: Smooth muscle tumors of uncertain malignant potential have an unpredictable clinical course, and relapses generally appear to occur after a long disease-free interval of up to several years. Therefore, patients diagnosed with smooth muscle tumors of uncertain malignant potential should receive long-term follow-up.