Huge soft tissue PEComa with aggressive lung and bone metastases

Perivascular epithelioid cell tumors (PEComas) are uncommon mesenchymal tumors characterized by the presence of both myogenic and melanocytic markers, and huge soft tissue PEComas are even rarer. With low prevalence, there has been no common consensus therapy in the past and the treatment response varies. As the aberrant activation of mammalian target of rapamycin (mTOR) pathway has been revealed in previous studies, mTOR inhibitor is now one of the treatment choices in malignant PEComa. Here we report a case of a 50-year-old man with identified 16-cm soft tissue mass at left flank with multiple lung and bone metastases, revealing typical immunohistochemical and pathological of malignant PEComa. Sirolimus was applied in an adjuvant setting, however interval progression in size was observed. To find the optimal dose of mTOR inhibitors, we performed a literature review for dosing strategy as well.