Liposarcoma

Liposarcoma (syn.: myxoma lipomatodes maligna, myxoides liposarcoma) is a malignant tumor of adipose tissue, rarely developing in the subcutaneous tissue, especially in the intermuscular fascia of the thighs with subsequent invasion of the subcutaneous fat layer. It never develops from lipoma, metastasizes mainly to the lungs and liver.

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Pathomorphology of liposarcoma

Liposarcoma has a pronounced variability of morphological structure, depending on the degree of differentiation of its component cellular elements. The following types of cells are distinguished in liposarcoma: mucoid lipoblasts with spindle-shaped nuclei and small sudanophilic droplets in the cytoplasm (with a certain degree of differentiation), mucoid lipoblasts with bizarre nuclei and the absence of fat droplets in the cytoplasm (with a high degree of anaplasia), located in the mucoid stroma, partially differentiated lipoblasts with spindle-shaped nuclei and coarsely vacuolated cytoplasm; well-differentiated cells with single large vacuoles and spindle-shaped nuclei located eccentrically; mature fat cells; cells with rounded nuclei located in the center and multiple vacuoles in the cytoplasm; giant cells with bizarre nuclei.

Depending on the predominance of one or another type of cell, WF Lever and G. Schanmburg-Lever (1983) distinguish four types of liposarcoma: highly differentiated, myxoid round cell and pleomorphic. Relatively highly differentiated liposarcoma resembles a lipoma consisting of cells of various sizes with one vacuole and hyperchromatic nuclei. Between them are cells with large, hyperchromatic and pleomorphic nuclei.

Myxoid liposarcoma is divided into high- and low-differentiated types. Myxoid liposarcoma type 1 contains few myxoid cells, predominantly lipoblasts with spindle-shaped nuclei and small sudanophilic droplets in the cytoplasm, highly differentiated fat cells and spindle-shaped lipoblasts with coarsely vacuolar cytoplasm. Myxoid liposarcoma type 2 is dominated by myxoid lipoblasts with bizarre nuclei and a small amount of sudanophilic substance. The stroma is scanty, mucoid in appearance, which makes this type of liposarcoma similar to myxosarcoma or undifferentiated fibrosarcoma.

Round cell liposarcoma is characterized by the presence of tightly packed, round or oval cells with one vacuole (signet ring cells) and lipoblasts with multiple vacuoles. Their nuclei are large, hyperchromatic and atypical, often in a state of mitosis.

Pleomorphic liposarcoma consists mostly of pleomorphic, giant multivacuolar lipoblasts with one or (usually) several hyperchromatic nuclei. Among them are small, polygonal, round or spindle-shaped lipoblasts. In some cases, the presence of a large number of vacuoles in the lipoblasts gives them an atypical appearance and resemblance to a mulberry. This gives grounds to classify this type of liposarcoma as a malignant hibernoma.

How is liposarcoma diagnosed?

The diagnosis of liposarcoma is based on the presence of lipids in the tumor, but in the pleomorphic and round cell types, due to the absence of sudanophilic substance, the detection of intracellular hyaluronidase-labile mucoid inclusions, revealed by staining with alcian blue, is of diagnostic value. Liposarcoma also contains hyaluronic acid, similar to embryonic adipose tissue, and quite often glycogen. Liposarcoma is differentiated from immature rhabdomyosarcoma and systemic multicentric myoblastosis, which affects subcutaneous adipose tissue and internal organs.