myolipoma
Myolipoma is a rare tumour, most often occurring in retroperitoneum/pelvis in adult females, which consists of an admixture of mature adipocytes and well-differentiated smooth muscle.
References
The evolving classification of soft tissue tumours: an update based on the new WHO classification. Fletcher CD. Histopathology. 2006 Jan;48(1):3-12. PMID: #16359532#