Soft Tissue Tumour Online
Pathology of Liposarcoma
Represents 40-45% of all liposarcoma.
Commonly occurs in the retroperitoneum or the limbs and rarely in the
spermatic cord and the mediastinum.
The behaviour of these lesions is substantially different depending on the location of the tumour.
Tumour in somatic soft tissue may recur but is incapable of distant metastasis and there is no tumour related death.
Tumour in retroperitoneum have a high incidence of recurrence.
The recurrent tumours may have 'dedifferentiated' appearance. Some of these patients
die as a result.
Subtypes according to histopathological features:
1. Adipocytic (lipoma like)
1. Adipocytic (Lipoma like ) -
Large well cicumscribed and coarsely lobulated tumour.
Microscopically, there are mature adipocytes showing variation in cell size. Focally nuclear atypia is evident.
In areas individual nuclei are compressed to crescentic shape.
Some hyperchromatic stromal cells are present. Lipoblasts may or may not be present.
Note: Presence of lipoblasts is not diagnostic of liposarcoma.
2. Sclerosing -
These are relatively pale and firm lesions occur most frequently in the retroperitoneum and the paratesticular region.
Microscopically, there are scattered hyperchromatic stromal cells, multivacuolated lipoblasts set in a collagenous backround.
Foci of atypical lipomatous elements are noted.
Prominent aggregates of lymphoid cells and plasma cells are noted simulating inflammatory pseudotumour.
4. Spindle cell-
There is proliferation of bland spindle cells in a fibrous or myxoid backround together with atypical lipomatous component including lipoblasts.
The differential diagnosis include: malignant peripheral nerve sheath tumour, spindle cell lipoma , neurofibroma (S100 positive), dermatofibrosarcoma protuberans (diffuse CD34 positive) , well differeniated sclerosing liposarcoma and low grade fibromyxoid sarcoma.
Cytogenetics- Ring or long marker chromosome derived from q13-15 region of chromosome 12.
Rare form of liposarcoma (5% of liposarcomas) usually located in the limbs of older adults.
These are aggressive tumours showing distant metastasis and about 40% mortality rate.
- A high grade pleomorphic MFH-like sarcoma containing few, scattered multivacuolated lipoblasts.
Careful sampling is necessary to identify these cells.
- A cellular pleomorphic or spindle cell neoplasm containing sheets of large bizarre lipoblasts.
Numerous intracytoplasmic eosinophilic globules may be present.
- Sometimes a heavy neutrophilic infiltrate is present. This lesion may cause diagnostic confusion with well differentiated inflammatory liposarcoma.
- A new variant of pleomorphic liposarcoma characterised by sheets of epithelioid cells and focal adipocytic differentiation.
Myxoid and Round
Represents 30-35% of all liposarcomas.
Myxoid and round cell liposarcomas commonly occur in the limbs usually between third and fifth decade.
1) Purely Myxoid Liposarcoma (Low Grade Tumour)-
Purely myxoid liposarcoma (low grade tumour) is characterised by hypocellular bland spindle cells in a myxoid backround.
Univacuolated lipoblasts are noted around the vessels.
Multivacuolated lipoblasts are present in the peripheral subcapsular zone.
There are thin walled branching vessels arranged in a plexiform pattern ('crow's feet' or 'chicken wire pattern' )
Mitotic figures are extremely scarce.
2) Myxoid / Round Cell Liposarcoma-
Myxoid/round cell liposarcoma is characterised by hypercellular areas with undifferentiated round cells.
These cells are larger with hyperchromatic and more rounded configuration, in contrast to the spindle cells in the myxoid variant.
Mitotic figures are more frequent.
These tumours have an aggressive behaviour.
Transition to hypercellular (round cell) areas are noted in myxoid liposarcoma.
3) Pure Round Cell Liposarcoma-
Pure round cell liposarcoma is rare (more than 80% round cells).
More than 10% round cell areas - increased potential for metastasis.
More than 25% round cell areas - High grade tumour.
Round cell liposarcoma - Differential diagnosis: Metastatic carcinoma, lymphoma, melanoma, Ewing's sarcoma.
Undifferentiated round cells and bland spindle cells in myxoid and round cells display cytoplasmic and nuclear positivity with S100 protein.
The lipoblasts stain positively with S100 protein.
Plexiform vascular areas may be demonstrated by CD31 and CD34 immuno- stains.
Cytogenetics- t(12;16) (q13;p11) with rearrangement of the CHOP gene.
The transition is usually abrupt in nature.
90% cases occur in primary tumour.
10% cases occur in recurrent tumour.
-May exhibit heterologous differentiation (myogenic, osteochondrosarcomatous or angiosarcomatous).
-New variant has been described exhibiting neural-like or meningothelial-like whorls of spindle cells.
Rarely paraganglioma-like histologic pattern has been observed.
- Sometimes the tumour exhibits fascicles of bland spindle cells these are described as low-grade areas.
- Spindle cell liposarcoma which represents lipogenic lesion,must be distinguished from low grade dedifferentiated liposarcoma which is non lipogenic in nature and has a relatively better prognosis.
- High grade dedifferentiated liposarcoma (non lipogenic) must be differentiated from pleomorphic liposarcoma.
- There is no difference in biological behaviour of low and high grade dedifferentiated liposarcomas.
These are associated with 20-25% metastasis.
Recurrence rate is usually high.
Distant metastasis in retroperitoneal dedifferentiated liposarcoma is rare and rapidly fatal: a clinicopathological study with emphasis on the low-grade myxofibrosarcoma-like pattern as an early sign of dedifferentiation.
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