Retroperitoneal lipo-leiomyomata in a woman with history of breast cancer and antiestrogen therapy.

Abstract

e22542 Background: Retroperitoneal lipo-leiomyomata are extremely rare. The usual-type retroperitoneal leiomyoma is itself a rare tumor that is mistaken preoperatively for malignant retroperitoneal tumors or thought of as an exophytic subserosal leiomyoma of the uterus. Lipo-leiomyoma is a variant of leiomyoma with an incidence in uterus ranging between 0.03% - 0.2%, but its presentation as a retroperitoneal mass has not been documented in literature yet. We present a unique case of retroperitoneal lipo-leiomyoma that presented as a diagnostic challenge due to its unique location and unusual histologic appearance. Methods: A 68-year-old female patient with a history of breast cancer diagnosed 4 years ago, currently on antiestrogen therapy (Fulvestrant) and Herceptin, presented to our university hospital with symptomatic left pelvic mass. An abdominal CT showed a heterogeneous low-density pelvic mass with foci of internal calcification and fat with surrounding intermixed intermediate and high density fluid in the expected location of the uterus. Results: A debulking surgery including radical hysterectomy was planned. Intraoperatively, a normal sized uterus was found, the myometrium of which contained multiple variable-sized intramural leiomyomata. In addition, a huge left retroperitoneal mass was found that had no connection to the uterus. Histopathological examination revealed abenign lipoleiomyomatous tumor, composed of an encapsulated proliferation of benign adipocytes and myoid cells intimately admixed. Immunohistochemistry confirmed myoid differentiation, with negative reactions for HMB45 and CKIT, and . MDM2 gene amplification by fluorescence in situ hybridization (FISH) was negative. Conclusions: Some unusually located extra-uterine leiomyomata have been reported; retroperitoneal leiomyoma being among them. Such a tumor with the added feature of lipomatous differentiation presents a differential diagnosis that includes leiomyosarcoma, liposarcoma, angiomyolipoma, and gastrointestinal stromal tumor. The association of an uncommonly located leiomyoma with subsequent lipomatous change withantiestrogen therapy is an unexplored issue that merits further investigation.