This video details the case of a large, deep, heterogeneous soft tissue mass in the buttock of a 70-year-old woman, highly suspicious for high-grade sarcoma based on MRI and gross findings (necrosis, hemorrhage, mixoid areas). Microscopic examination confirms the diagnosis of Pleomorphic Liposarcoma (PLPS), a high-grade malignancy defined by the presence of pleomorphic lipoblasts—cells containing clear, scalloping vacuoles that indent the nucleus. The pathologist highlights the wide morphological variation within the tumor (spindle cells, epithelioid areas) and discusses key diagnostic differentiations (particularly from dedifferentiated liposarcoma based on location/MDM2 status). PLPS is noted for its highly aggressive nature and poor prognosis when deep-seated (5-year survival ~50%), contrasting sharply with its much better behavior when found in the skin or subcutis.
Case Study: Pleomorphic Liposarcoma (PLPS) of the Buttock
0:11 Case Introduction: A 70-year-old woman presented with a large, deep soft tissue mass in the buttock musculature.
0:22 Imaging and Gross Pathology: MRI showed a large, heterogeneous, lobulated mass, highly concerning for high-grade sarcoma. Grossly, the mass was heterogeneous, containing mixoid/gelatinous areas, firm white/fleshy areas, cystic spaces, necrosis, and hemorrhage.
1:36 Microscopic Appearance: Low-power microscopy revealed highly cellular zones with areas of necrosis and hemorrhage, consistent with the gross findings.
2:15 Diagnosis: The tumor was diagnosed as Pleomorphic Liposarcoma (PLPS), defined as a high-grade sarcoma containing pleomorphic lipoblasts.
2:25 Morphological Heterogeneity: PLPS exhibits a wide range of patterns, including pleomorphic spindle cells (resembling Undifferentiated Pleomorphic Sarcoma), epithelioid, and round cell areas.
3:16 Key Diagnostic Feature (Lipoblasts): True lipoblasts contain lipid droplets that dissolve during processing, leaving sharp, clear holes/vacuoles. These vacuoles characteristically push against and indent (scallop) the nucleus, creating a signet-ring appearance.
4:47 Additional Histologic Clue: The pathologist notes observing pink, hyalinized proteinaceous droplets frequently within PLPS cells, which can prompt a search for associated lipoblasts.
5:54 Differentiation (Location Matters): High-grade sarcoma with lipoblasts in an extremity (like the buttock) is typically PLPS. If the tumor were in the retroperitoneum, dedifferentiated liposarcoma (DDLPS) would be the primary consideration. Differentiation can be confirmed using MDM2 testing (FISH or immunostain).
6:22 Treatment Approach: Treatment for PLPS is similar to other high-grade pleomorphic sarcomas (surgical removal with negative margins, often followed by radiation or chemotherapy). Targeted chemo therapies are currently limited (as of Jan 2022).
9:19 Non-Specific Features: The tumor displayed dilated, almost staghorn vessels (hemangioparasitic vascular pattern), which is a classic feature of Solitary Fibrous Tumors but is not specific to SFT and can be seen in many other tumor types.
11:09 Molecular Characteristics: PLPS, like many pleomorphic sarcomas, lacks a recurrent molecular abnormality, instead showing random chromosomal gains and losses (aneuploidy).
11:36 Prognosis (Deep-Seated): PLPS is highly aggressive, carrying a higher risk of metastasis than many other adult pleomorphic sarcomas. The 5-year survival rate is approximately 50%.
12:07 Unique Superficial Behavior: PLPS is the most uncommon major subtype of liposarcoma overall, but it is the most common subtype to involve the skin/subcutis. When located superficially, it behaves much better, often resulting in a better prognosis.