PMC5362705_01
Imaging data of the different occurrences of the tumor: Gadolinium enhanced T1-weighted MR sequence, coronal section (a), Gadolinium enhanced T1-FATSAT weighted MR sequence, parasagittal (g), and axial sections (h), CT scan without injection, axial sections (b), T1-weighted MR sequence, parasagittal sections (c and e), and T1-FATSAT weighted MR sequence, axial section (d and f). There was no obvious radiological connection of the mass with the underlying bone, ruling out a surface tumor. Histological areas corresponding to bone formation were seen as calcified clusters on CT scans, surrounded by a peripheral rim of tumorous fat identified as hypersignal in T1-weighted RM sequences. The two local recurrences showed similar features; however, the ossified core was more homogeneously calcified compared to the first occurrence.
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CT scan showed an 8 x 4 x 4 cm tumorous mass lying in the paravertebral left muscles and composed of a central hyperdense core and a lower density rim (Figure 1(b)). MR imaging showed that the tumor combined a peripheral fatty component surrounding an ossified core (Figure 1(b)). CT and MR imaging of these two recurrences are shown in Figures 1(c)to 1(h).
Histological features of the first occurrence: general view of the tumor. A central zone of osteogenesis forms an ossified core intermixed with a low-grade fibroblastic component all of which is surrounded by a mature lipogenic component that extends to the margins of the tumor.
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Microscopically, distinct histological patterns were present (Figure 2): a main component (80%) composed of areas of osteogenesis and a minor peripheral component (20%) of well-differentiated adipose tissue, both of which were intermingled with an abundant fibroblastic stroma.
Histological features of the different occurrences of the tumor. (a) Well-differentiated liposarcoma component, first occurrence. Lipogenic clusters are entrapped within a stromal proliferation composed of fusiform cells. A cluster of bone formation is obvious. (b) Low-grade osteosarcoma component, first occurrence. The osteogenic areas are composed of long trabeculae of woven bone associated with the same proliferation of fusiform stromal cells in the intertrabecular spaces. These stromal cells are fusiform, elongated with moderate nuclear atypias. These morphological findings are very similar to low-grade osteosarcoma. (c) and (d) Histological aspects of the recurrences. The 2011 recurrence (c) and the 2014 recurrence (d) showed very similar histological findings compared to the first occurrence of the tumor.
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Bone-forming areas were arranged in long, parallel, and narrow trabeculae of woven bone surrounded by a low-grade population of spindle cells similar to what is commonly observed in low-grade osteosarcoma (LGO) (Figure 3(b)). The fatty component was composed of mature anisocytic adipocytes arranged in lobules, with rare spindle cells within their septa that displayed large hyperchromatic nuclei, a morphological finding usually observed in low-grade ALN/WDL (Figure 3(a)). On both of the resected specimens, histological features were identical to the first resection with subtle variation in the proportion of the two components (Figures 3(c) and 3(d)).
Immunostaining of MDM2, CDK4, and P16: (a), (b), and (c) Immunostaining with anti-MDM2 antibody. MDM2 nuclear positivity is present in 5-10% of stromal cells (a), in some lipoblasts (b), and in rare osteoblasts rimming neoformed bone (c). (d) Immunostaining with anti-CDK4 antibody: more diffuse nuclear but also cytoplasmic staining was present in stromal cells and osteoblasts (20-30%). (e) Immunostaining with anti-P16 antibody: albeit not specific, diffuse and strong positivity with P16 was present in stromal cells, cells rimming or within bone trabeculae and also in lipoblasts.
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Immunostains showed that the osteogenic, lipogenic, and fibrogenic territories displayed nuclear overexpression of MDM2 (Figures 4(a), 4(b), and 4(c)) and CDK4 (Figure 4(d)), with 5-10% and 20-30% of nuclei stained, respectively. P16 was overexpressed by all tumors cells, with an intense and diffuse pattern of expression (Figure 4(e)).