Ross et al. Journal of Medical Case Reports 2011, 5:383 http://www.jmedicalcasereports.com/content/5/1/383 Page 4 of 6 Figure 2 MRI scan of the pelvis after two years on sirolimus, demonstrating a reduction in size of the perivascular epithelioid cell tumor (PEComa) (measuring 53 mm) following treatment with sirolimus. melanosomes. In this case the tumor cells expressed HMB45, melan A and smooth muscle actin. PEComas of the gynecological tract account for approximately 40% of reported cases [3]. In the pelvis, the uterine body appears to be the most prominent site of this rare tumor, with smaller numbers of PEComas reported in the broad ligament, pelvic soft tissue, cervix, vagina and the urinary bladder [4-7]. Morphologically there are two types, epithelioid and spindle cell. In the epithelioid type the cells have clear to lightly eosinophilic, finely granular cytoplasm and may form thick-walled pseudo blood vessels. The spin- dle cell type, which has fascicles and nests of spindle cells with clear to lightly eosinophilic cytoplasm arrayed around an elaborate capillary sized vascular network, forms the majority of cases [4]. Uterine PEComas are characterized by perivascular epithelioid cells that are HMB45 positive/S-100 protein negative with abundant clear to eosinophilic granular cytoplasm, but there may be an overlap with some epithelioid smooth muscle tumors of the uterus making the initial diagnosis difficult [8]. The patient’s lesion is