A well-differentiated liposarcoma co-existent with leiomyoma.

Background: The coexistence of a well-differentiated liposarcoma (atypical lipomatous tumor) and benign smooth muscle component in a single soft tissue neoplasm is extremely rare.

Case Report: Histologic and immunohistochemical characteristics of tumor, which represented the recurrence of a retroperitoneal atypical lipoma in a 50-year-old female patient are presented in this paper. The tumor represented the recurrence of a retroperitoneal atypical lipoma. Lipomatous component consisted of a mixture of lipoma-like and sclerosing variant of well-differentiated liposarcoma. Characteristically, the heterologous smooth muscle differentiation was manifested as a macroscopically visible nodular growth in the form of a leiomyoma within the adipocytic component. It consisted of intersecting fascicles of spindle cells, which lacked mitoses and significant atypia, and were immunopositive for smooth muscle markers.

Conclusion: This case of well-differentiated liposarcoma with benign smooth muscle is the first reported tumor of retroperitoneal localization. It is also the first one to exhibit the heterologous smooth muscle component as a distinct leiomyoma.