Microscopic description and IHC:
Grossly, this is a 5.5 cm multinodular, tan-white paratesticular mass. Histologically, there are 2 components. The well differentiated liposarcoma component features fibrous septa and hypocellular collagenous stroma with scattered pleomorphic and spindle cells and surrounding lipocytes of varying sizes. The dedifferentiated component consists of a solid sheet of spindle cells with hyperchromatic nuclei. There is also a prominent lymphocytic infiltration, highlighted by CD45. On immunohistochemical stains, the tumor cells are negative for AE1/3, S-100, and CD31. There is focal positivity for SMA in the dedifferentiated component. MDM2 and CDK4 are positive. MDM2 gene amplification was detected by fluorescent in situ hybridization.
Discussion:
Well-differentiated liposarcoma is the most common sarcoma of the paratesticular soft tissue including the spermatic cord. Dedifferentiated liposarcoma, in contrast, is quite rare. The diagnosis is made when the well-differentiated and dedifferentatied components are both identified histologically. The well-differentiated component consists of fibrous septa containing atypical cells with large hyperchromatic nuclei. Various sized adipocytes are also identified. Lipoblasts are not required. The dedifferentiated component is comprised of a solid focus that can be low or high grade based on cellularity, necrosis and mitotic rate, with various histological patterns. This component is devoid of adipocytes. MDM2 and CDK4 positivity are helpful in making the diagnosis.
These tumors tend to develop in older men in, contrast to benign lipomas that are found in a large age range. Complete resection with negative margins is often difficult on first attempt. Recurrence rates have varied from 22.6%-41% with metastatic rates ranging from 6.5%-17%. Tumor grade may have prognostic significance with high-grade tumors having higher likelihood of recurrence and worse disease-specific survival.