Clinical features: age 40-60 years, M=F; extremely rare in childhood.
Gross: Generally large tumors (>5cm); well circumscribed yellow-white with lobulated cut surface which may appear fatty or fibrotic (image A).
Amplified sequence of Chr 12q14-15 (amplification of MDM2 and CDK4).
Most often are well-differentiated LPS.
"Lipoma-like", most common, simulates lipoma except for scattered lipoblasts (immature adipocytes) with atypical hyperchromatic nuclei (image B) and adipocytes show more variability in size and shape than would be expected in a lipoma (image C) & (image D).
Sclerosing type, scattered bizarre cells and lipoblast in collagenous stroma.
Inflammatory type, lipoblasts, adipocytes, and inflammatory infiltrate of lymphocytes and plasma cells.
Other types of liposarcoma such as pleomorphic, myxoid or round cells are very rare in retroperitoneum.
Immunohistochemistry: S100+, nuclear MDM+ and CDK4+.
Prognosis: These are low-grade tumors that never metastasize – although they can recur, may dedifferentiate (~20%), and THEN metastasize.
Retroperitoneal LPS often recur because of difficulty for adequate surgical excision.