Liposarcoma C49.-

Malignant soft tissue tumor located in the skin and subcutis which is an extremely rare rarity in dermal or dermal/subcutaneous localization. Liposarcomas of the deep soft tissues of the extremities can be diagnosed via the Integument.

Depending on the degree of cell atypes are distinguished:

1. Atypical lipomatous tumor/highly differentiated liposarcoma (sclerosing or inflammatory) (40-45% of cases)
2. Progression into a dedifferentiated liposarcoma (10% of cases)
3. Myxoid/round cell liposarcoma (15 - 20% of cases)
4. Pleomorphic liposarcoma (5% of cases)
5. Spindle cell liposarcoma

• Common to all highly differentiated liposarcomas is a ring chromosome or alterations of chromosome 12.
• In the group of myxoid or round cell liposarcomas, characteristic chromosomal aberrations are reciprocal translocations which lead to new gene fusions. Translocation between chromosomes 12 and 16; t (12; 16) (q13; p11). Affected are the CHOP gene (C/EBP-homologous protein) on chromosome 12q13 and the TLS gene (translocated in liposarcoma)/FUS (fusion) on chromosome 16. The fusion protein (TLS/FUS-CHOP fusion transcripts) resulting from t (12; 16) (q13; p11) acts as a transcription factor and thus plays a role in the oncogenesis of these liposarcoma subtypes.
• No uniform chromosomal aberrations have been described for the pleomorphic liposarcoma.

Typical for all forms are atypical cells in combination with lipoblasts. The cell nucleus is deformed by fat vacuoles in a seal-ring-like to star-shaped manner. This results in bizarre, hyperchromatic nuclear formations. Occasionally, micropseudocysts also develop. The vascular richness with a plexiform vascular pattern is striking.

Immunohistology: Reactivity to S100.

4 types of highly differentiated liposarcomas are distinguished:

• Lipoma-like highly differentiated liposarcoma
• Sclerosed highly differentiated liposarcoma
• Inflammatory highly differentiated liposarcoma
• Spindle cell highly differentiated liposarcoma.

The prognosis for large liposarcomas localized in deep soft tissue is very unfavorable and often characterized by early metastasis in liver and lungs. The 5-year survival rate for myxoid liposarcomas is 90%, that of pleomorphic liposarcomas 20%.

The rare, purely dermal tumours have a favourable prognosis.

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