Sections reveal well-demarcated, multinodular tumor divided into distinct lobules by dense fibrous septa. The tumor cells are uniformly small to medium-sized and are arranged in interconnecting cords, strands, and loose reticular networks embedded within a prominent, pale basophilic myxoid matrix. The tumor cells exhibit round to oval, relatively monomorphic nuclei with evenly distributed chromatin and scant, eosinophilic to slightly vacuolated cytoplasm; anaplasia and mitotic activity are mild. Margins are free.
The morphologic differential diagnosis for this myxoid soft tissue lesion primarily includes extraskeletal myxoid chondrosarcoma, myoepithelial carcinoma of soft tissue and myxoid liposarcoma with round cell component. Definitive diagnosis requires an immunohistochemical panel comprising (S100 protein, LCA, EMA, CK, MDM2, p63, and CD34) for definitive diagnosis.
Progressively enlarging, recurrent right posteromedial upper thigh mass at the site of a prior excision five years ago.
A single soft tissue mass measuring 14 x 12 x 12.5 cm was partially covered by skin measuring 8.5 x 4 cm, and upon sectioning revealed a solid firm greyish-colored mass measuring 13 x 11 x 9.5 cm that was located 3 cm away from the skin margin and 0.5 cm from the deep margin.
Right posteromedial upper thigh mass, excision: