Liposarcoma pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]Sabawoon Mirwais, M.B.B.S, M.D.[3]

Liposarcoma is the most common sarcoma of soft tissue. The pathogenesis of liposarcoma depends on the histological sub-type. The two sub-types, well differentiated and dedifferentiated, are the two most commonly occurring liposarcomas. The majority of well differentiated liposarcomas arise in the retroperitoneum. The chromosome region 12q13-15, is rich in protooncogenes, including the CHOP, CDK4, MDM2, HMGI-C, GLI, SAS, OS1, and the OS9, all of which play an important role in the pathogenesis of many neoplasms. Liposarcoma is associated with genetic conditions like Li-Fraumeni syndrome. Liposarcoma usually presents as a mass which often resembles lipoma and is multinodular. Microscopic pathological findings of liposarcoma depend on the sub-type.

• Liposarcoma is the most common sarcoma of soft tissue.^[1]
• The two sub-types, well differentiated and dedifferentiated, are the two most commonly occurring liposarcomas.^[2]
• The majority of well differentiated liposarcomas arise in the retroperitoneum.^[3][4]

• The tumor can also arise in the deep soft tissue of the thigh, mediastinum, and paratesticular area.^[5][6]

• Retroperitoneal tumors are more likely to recur.^[7][8]
• The dedifferentiated sub-type arises as a primary or de novo lesion in majority of the cases.^{[9][10][11][12]}

• The dedifferentiated sub-type is clinically more aggressive than the well differentiated liposarcoma.^{[13][14][15][16]}

• The chromosome region 12q13-15, is rich in protooncogenes, including the CHOP, CDK4, MDM2, HMGI-C, GLI, SAS, OS1, and the OS9, all of which play an important role in the pathogenesis of many neoplasms.
• Amplification of some of these regions, with concomitant amplification of their proteins, has clearly been demonstrated in liposarcoma.^[17]
• The difference between malignant and benign masses resides in the amount of rearranged gene present in each tissue.^[17]

• Liposarcoma is associated with genetic conditions like Li-Fraumeni syndrome.

• Liposarcoma usually presents as a mass which often resembles lipoma and is multinodular.
• Cut surface may be soft or firm and is yellow in color.
• Focal mucinous area may be seen.
• Areas of necrosis may be noted.

Each liposarcoma sub-type has specific characteristics:

• The particular histological finding in this type of well differentiated liposarcoma is the identification of distinctive stromal cells distributed across the tissue, which are associated with lipoblasts filled with multiple vacuoles.
• This association forms a collagenous background of fibrillary appearance.
• In certain cases, the fibrous component of the neoplasm may occupy most of its mass.^[18]

• Frequently composed by adipocytes with different cell sizes, hyperchromasia, and nuclear atypia.
• Fibrous septa may be identified surrounding adipocytes, containing hyperchromatic stromal cells.
• Besides these two types of cells, mono- or multi-vacuolated lipoblasts may also be identified.
• Lipoblasts are characterized by the presence of single (mono) or multiple (multi) peripheral cytoplasmic vacuoles that press on the hyperchromatic nucleus.^[18]
• In general, adipocytic neoplasms are often identified by the presence of these lipoblasts.
• Additionally, lipoblasts may infrequently be absent, which makes the diagnosis of adipocytic neoplasm more difficult but possible with the help of other histological features.^[18]

• Its adipocytic nature may be misidentified due to the heavy chronic inflammatory infiltrate.
• The inflammatory component is frequently composed of different lympho–plasmacytic aggregates. These tend to be predominantly formed by a specific type of B-cell, or less commonly T-cells may populate the inflammatory aggregate.^[18][19][20]

• This is a rare adult-type of well-differentiated liposarcoma.
• It results from the proliferation of neural-like spindle cells, which are organized in a fibrous structure, that contains lipoblasts.^[21][22]

• In this form of liposarcoma, there is a transition from a low-grade differentiation to a high-grade differentiation within the same mass of well-differentiated liposarcoma.^[18][23][24]
• 90% of dedifferentiation from well-differentiated liposarcomas occur in primary tumors, while the remaining 10% occur in recurrent neoplasms.^{[25][26][27][28]}

• They have a non-homogenous appearance with cystic and solid components.

• It is a high-grade liposarcoma which is a poorly differentiated form of myxoid sarcoma.
• It has a very poor prognosis and often metastasizes to the retroperitoneum, pleural cavity, soft tissue, or pelvis and very rarely to the lungs.
• Microscopically, it consists of small, round, or spindle cells with sparse eosinophilic and granular cytoplasm and large nuclei.
• It may have scattered lipoblasts and areas of necrosis.

• Pleomorphic cells may be identified with enlarged round to bizarre nuclei.

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