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Pathology & Laboratory Medicine

URMC / Pathology & Laboratory Medicine / Education / Case of the Month / Case 58: Recurrent Chest Wall Mass / Diagnosis

 

Diagnosis & Discussion

Diagnosis

Recurrent pleomorphic liposarcoma, epithelioid variant.

Discussion

Pleomorphic liposarcoma (PLS), according to the World Health Organization (WHO) classification, is by definition a pleomorphic, high-grade sarcoma containing a variable number of pleomorphic lipoblasts and with a complex genomic profile. No areas of atypical lipomatous tumor/well-differentiated liposarcoma or other line of differentiation is present.

PLS is the rarest type of liposarcoma and accounts for approximately 5% of liposarcoma cases. PLS tends to occur in patients older than 50-years of age and most commonly occurs in the extremities (lower more frequently) as a deep seated mass. Other sites of involvement include the trunk, retroperitoneum, and spermatic cord. PLS has rarely been reported to involve the mediastinum, heart, pleura, breast, scalp, colon, and orbit. PLS frequently recurs locally and metastasizes to the lungs. PLS is an aggressive tumor with a poor prognosis and complete surgical resection is the treatment of choice. Postoperative radiation may be utilized for large or incompletely resected tumors.

Histologically, the tumor cells are composed of lipoblasts, which are the essential feature. Morphological patterns of these tumors include: pleomorphic, myxofibrosarcoma-like, and epithelioid. Epithelioid morphology may be seen in around 25% of cases. The main finding in PLS is pleomorphic lipoblasts with enlarged to pleomorphic nuclei and cytoplasmic vacuoles. The epithelioid variant of PLS demonstrates solid, cohesive sheets of epithelioid cells with clear to eosinophilic or vacuolated cytoplasm. Necrosis is found in all patterns of PLS. By immunohistochemistry, the lipoblasts can be positive with S-100 (less than half of cases) and the epithelioid variant may express keratin and epithelial membrane antigen (EMA) focally. Smooth muscle actin (SMA) and CD34 may be positive, usually focally, in nearly half of cases.

Depending on the morphologic subtype the histologic differential diagnosis includes undifferentiated pleomorphic sarcoma (much overlap, no definite lipoblasts), dedifferentiated liposarcoma, (MDM2 and CDK4 positive by immunohistochemistry, or MDM2 amplification by fluorescence in situ hybridization), myxofibrosarcoma (more commonly subcutaneous, multinodular, no lipoblasts, mucin-containing pseudolipoblasts), and carcinoma. The epithelioid variant of PLS can bear resemblance to clear renal cell carcinoma or adrenocortical carcinoma (both will have more than focal expression of epithelial markers). Melanoma should also be excluded.

In summary, PLS is the least common variant of liposarcoma but tends to have an aggressive clinical course. PLS most commonly affects the deep soft tissue of the lower extremities. PLS, by definition, is a high-grade sarcoma with pleomorphic lipoblasts but no atypical lipomatous tumor/well-differentiated liposarcoma component. There are three common variants: pleomorphic (most common), myxofibrosarcoma-like, and epithelioid. The histologic differential diagnosis of the epithelioid variant is mainly with clear cell carcinomas including, but not limited to, adrenocortical or clear cell renal cell carcinoma. Surgical resection is the primary modality of treatment.

References

  1. Coindre J-M. Pedeutour F. In Fletcher CDM, Bridge JA, Hogendoorn P, Mertens F. (2013) WHO Classification of Tumours of Soft Tissue and Bone. Fourth Edition. Lyon, France: IARC.

  2. Downes, K., Goldblum, J., Montgomery, E. et al. Pleomorphic Liposarcoma: A Clinicopathologic Analysis of 19 Cases. Mod Pathol 14, 179-184 (2001). https://doi.org/10.1038/modpathol.3880280

  3. Lindberg, Matthew R. Pleomorphic Liposarcoma. https://app.expertpath.com/document/pleomorphic-liposarcoma/0ec77b95-c690-4a63-abb2-57042f3d62f6. Accessed June 22nd, 2021.

  4. Shankar V. Pleomorphic liposarcoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissueadiposepleomorphiclipo.html. Accessed June 22nd, 2021.

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