Malignant PEComa on the Lower Extremity

A 31-year-old female patient presented during our tumor orthopedic consultation hours with a mass accompanied by load-dependent pain in the ventromedial left lower leg as well as weight loss. Another center had initially suspected hematoma following a bicycle fall. Due to a progressive increase in size over the subsequent months, a magnetic resonance imaging investigation was finally performed (Figure a). Clinically, a firm elastic, non-movable mass that was painful on palpation was seen. The histology obtained via an incisional biopsy (Figure b) revealed a malignant PEComa (perivascular epithelioid cell tumor). After excluding metastatic spread by means of staging computed tomography, the tumor, together with a thin section of the tibia, was resected en bloc. At 12 months post surgery, the patient is thus far free of recurrence and without functional impairment. From a differential diagnostic perspective, both benign and malignant soft tissue tumors need to be considered. The treatment of choice is R0 resection, while radiotherapy is discussed for improved local control. In the case of metastasis, systemic treatment is of value. In the literature, the uterus, skin, liver, retroperitoneum, and colon are described as the primary sites of disease. Limbs represent an absolute rarity in terms of disease location.

Figure.

a) MRI of the left lower leg: axial, fat-suppressed T1-weighting: largely solid, contrast-enhancing soft tissue mass (6 × 6 × 3.5 cm) directly in contact with the ventromedial tibial crest

b) At high magnification (HE, 400 ×), one sees pleomorphic tumor cells with abundant cytoplasm, high-grade nuclear atypia (asterisk), and mitotic activity (arrow). PEComa are rare mesenchymal tumors of varying biological aggressiveness that develop from perivascular epithelioid cells.