Diagnosis -- High-grade Pleomorphic Liposarcoma.

FINAL DIAGNOSIS

High-grade pleomorphic liposarcoma.

DISCUSSION

Pleomorphic liposarcoma is a rare subtype of liposarcoma accounting for less than 5% of all liposarcomas. Most cases are seen in adults (7th decade of life) with a slightly higher incidence in males [1].

Clinically, these tumors grow rapidly and often are painless. Mostly, they are found in the extremities (more commonly lower limbs than the upper limbs). Most cases arise in the deep soft tissue with about 25% developing in the subcutaneous fat [2, 3].

Grossly, these tumors are large with an average size of 8 to 10 cm. They are often well-demarcated but non-encapsulated. Upon sectioning, these tumors tend to be white to yellow with myxoid changes and necrosis [4]. Histologically, most of these tumors will have infiltrative margins with varying proportions of pleomorphic lipoblasts in a background of high-grade, pleomorphic and undifferentiated sarcoma. The presence of pleomorphic lipoblasts is essential to the diagnosis although the number can vary per case. In our case, only scattered foci of pleomorphic lipoblasts were found, while most of the tumor was non-lipogenic and was comprised of areas reminiscent of undifferentiated pleomorphic sarcoma with multinucleated giant cells. Notable features that are commonly present in pleomorphic liposarcomas include presence of extremely large tumor cells often showing clear or vacuolated cytoplasm. Necrosis is present in more than half of the cases [5].

Unlike dedifferentiated liposarcoma with homologous differentiation which usually harbors pleomorphic lipoblasts, staining for MDM2 and CDK4 and amplification of MDM2 gene is negative in pleomorphic liposarcoma [6].

In conclusion, pleomorphic liposarcomas are rare high-grade tumors defined by the presence of characteristic pleomorphic lipoblasts within a background of a high-grade sarcoma with absence of MDM2 gene amplification. For reaching the correct diagnosis, it is essential to adequately sample the tumor and thoroughly search for these characteristic pleomorphic lipoblasts, especially that in some instances they can be rare, just like in our case, thus rendering this is a challenging diagnosis.

REFERENCES

1. Hornick JL. Subclassification of pleomorphic sarcomas: How and why should we care? Ann Diagn Pathol. 2018;37:118-24.
2. Downes KA, Goldblum JR, Montgomery EA, Fisher C. Pleomorphic liposarcoma: a clinicopathologic analysis of 19 cases. Mod Pathol. 2001;14(3):179-84.
3. Gebhard S, Coindre JM, Michels JJ, Terrier P, Bertrand G, Trassard M, et al. Pleomorphic liposarcoma: clinicopathologic, immunohistochemical, and follow-up analysis of 63 cases: a study from the French Federation of Cancer Centers Sarcoma Group. Am J Surg Pathol. 2002;26(5):601-16.
4. Hornick JL, Bosenberg MW, Mentzel T, McMenamin ME, Oliveira AM, Fletcher CD. Pleomorphic liposarcoma: clinicopathologic analysis of 57 cases. Am J Surg Pathol. 2004;28(10):1257-67.
5. Dei Tos AP. Liposarcomas: diagnostic pitfalls and new insights. Histopathology. 2014;64(1):38-52.
6. Dreux N, Marty M, Chibon F, Velasco V, Hostein I, Ranchere-Vince D, et al. Value and limitation of immunohistochemical expression of HMGA2 in mesenchymal tumors: about a series of 1052 cases. Mod Pathol. 2010;23(12):1657-66.

Contributed by Simmi Patel, MD and Rana Naous, MD