Fig. 1

A Computed tomography reveals a mass (red circle), with a diameter measuring up to 5 cm, in the anterior mediastinum. B Gross image of the resected specimen showing a yellowish and whitish mass measuring 75 mm × 43 mm × 28 mm (scale bar = 10 mm). C Light micrograph of a hematoxylin–eosin-stained resected tissue specimen of the red square from Fig. 1B (scale bar = 5 mm). D High-power view of the selected area (red square) from Fig. 1C. Visible is a mixture of uniform round to oval-shaped non-lipogenic cells and small lipoblasts in a prominent myxoid stroma, similar to that of a myxoid liposarcoma (scale bar = 100 μm). E High-power view of the selected area (yellow square) from Fig. 1C, showing pleomorphic lipoblasts containing enlarged and hyperchromatic nuclei, similar to that of a pleomorphic liposarcoma (scale bar = 100 μm). F High-power view of the selected area (green square) from Fig. 1C, showing adipocytic proliferation with moderate nuclear atypia in adipocytes and stromal cells, which is difficult to use to make differential diagnosis between well-differentiated liposarcoma and pleomorphic liposarcoma (scale bar = 100 μm). G High-power view of the selected area (blue square) from Fig. 1C, showing nests of atypical chondroid cells that contain enlarged nuclei with a myxohyaline stroma (scale bar = 100 μm). Light micrographs of immunohistochemical staining for various proteins. H p53 and I) c-myc are expressed in nuclei of atypical cells (scale bar = 50 μm). J Rb1 and K) MDM2 are negative in the nuclei of atypical cells (scale bar = 50 μm)