Liposarcomas Symptoms Notes

Adipocytic Tumours

Lipomas and liposarcomas are common examples of benign and malignant tumours respectively of adipose tissue. Uncommon varieties of adipose tissue tumours include hibernoma, a benign tumour arising from brown fat, and lipoblastoma (foetal lipoma) resembling foetal fat and found predominantly in children under 3 years of age.

Lipoma:

• Lipoma is the commonest soft tissue tumour. It appears as a solitary, soft, movable and painless mass which may remain stationary or grow slowly. Lipomas occur most often in the 4th to 5th decades of life and are frequent in females.
• They may be found at different locations in the body but the most common sites are the subcutaneous tissues in the neck, back and shoulder. A lipoma rarely ever transforms into liposarcoma.

Grossly, a subcutaneous lipoma is usually small, round to oval and encapsulated mass. The cut surface is soft, lobulated, yellowish-orange and greasy.

Read And Learn More: Systemic Pathology Notes

Histologically, the tumour is composed of lobules of mature adipose cells separated by delicate fibrous septa. A thin fibrous capsule surrounds the tumour. Spindle cell lipoma is an uncommon variant. Atypical lipoma is now considered synonymous with well-differentiated liposarcoma, an intermediate-grade locally aggressive tumour.

A variety of admixtures of lipoma with other tissue components may be seen. These include fibro-lipoma (admixture with fibrous tissue), angiolipoma (combination with proliferating blood vessels), myelolipoma (admixture with muscle tissue), and chondroid lipoma. Infrequently, benign lipoma may infiltrate the striated muscle (infiltrating or intramuscular lipoma).

Liposarcoma:

• Liposarcoma is one of the most common soft tissue sarcomas in adults. Unlike lipoma which originates from mature adipose cells, liposarcoma arises from primitive mesenchymal cells, the lipoblasts. The peak incidence is in the 5th to 7th decades of life.
• In contrast to lipomas which are more frequently subcutaneous in location, liposarcomas often occur in the deep tissues. The most frequent sites are intermuscular regions in the thigh, buttocks and retroperitoneum.

Grossly, liposarcoma appears as a nodular mass, 5 cm or more in diameter. The tumour is generally circumscribed but infiltrative. The Cut surface is grey-white to yellow, myxoid and gelatinous. Retroperitoneal masses are generally much larger.

Histologically, the hallmark of diagnosis of liposarcoma is the identification of the variable number of lip-oblasts which may be uni vacuolated or multivacuolated. The vacuoles represent fat in the cytoplasm. Four major histologic varieties of liposarcomas are distinguished: well-differentiated, myxoid, pleomorphic, and no otherwise specified:

1. Well-differentiated liposarcoma resembles lipoma (also called an atypical lipoma) but contains uni- or multi-vacuolated lip oblasts.
2. Myxoid liposarcoma is the most common histologic type. It is composed of monomorphic, fusiform or stellate cells representing primitive mesenchymal cells, lying dispersed in mucopolysaccharide-rich ground substance. Occasional tumour giant cells may be present.
   • The prominent meshwork of capillaries forming a chicken-wire pattern is a conspicuous feature Round cell variant composed of uniform, round to oval cells having fine multivacuolated cytoplasm with central hyperchromatic nuclei, is now considered a high-grade myxoid liposarcoma.
3. Pleomorphic liposarcoma is highly undifferentiated and the most anaplastic type. There are numerous large tumour giant cells and bizarre lip oblasts.
4. Liposarcoma not otherwise specified includes those rare and mixed morphologic patterns of liposarcoma that are categorised under this term.

• Myxoid liposarcoma and its round cell morphologic variant show the same cytogenetic abnormality of translocation t(12;16) (q13; p11) and molecular profiling of FUS-DDIT3 fusion gene, features which help in distinguishing these variants from other types.
• The prognosis of liposarcoma depends upon the location and histologic type. In general, well-differentiated and myxoid varieties have excellent prognoses, while pleomorphic liposarcoma has a significantly poorer prognosis.
• Round cell variants of myxoid liposarcoma and pleomorphic liposarcoma are high-grade tumours and metastasise frequently to the lungs, other visceral organs and serosal surfaces.

Adipocytic Tumours:

• Lipoma is the commonest soft tissue tumour appearing as a solitary, soft, movable and painless mass which may remain stationary or grow slowly.
• Liposarcoma occurs in the 5th to 7th decades of life and arises from primitive mesenchymal cells, the lip blasts. Unlike lipomas, liposarcomas often occur in the deep tissues.
• Histologic variants of liposarcoma have prognostic significance; these are well differentiated, myxoid (including round cell morphology), pleomorphic and unclassified type (NOS).