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Soft Tissue Pathology 

Pathology of Pleomorphic Undifferentiated Sarcoma (PUS) or Undifferentiad Pleomorphic Sarcoma

(Previously known as Malignant Fibrous Histiocytoma)

Dr Sampurna Roy MD                   

 

                                                                                                                      

 

 

Malignant fibrous histiocytoma (MFH) was regarded as the most common soft tissue sarcoma of the late adult life for almost 25 years.

Serious doubts have been raised about the existence of MFH as a specific entity.

Adults between 50-70 years  are usually affected.

According to the latest World Health Organisation classification of soft tissue tumours, so called malignant fibrous histiocytoma can no longer be regarded as a definable entity, and is now viewed as a synonym for undifferentiated pleomorphic sarcoma.

Old classification - Clinicopathological variants:

1.Storiform-Pleomorphic; 2. Myxofibrosarcoma  3.Inflammatory;  4.Giant cell ; 5.Angiomatoid

According to the next World Health Organisation classification of soft tissue tumours, so called malignant fibrous histiocytoma can no longer be regarded as a definable entity, and is now viewed as a synonym for undifferentiated pleomorphic sarcoma.

- Undifferentiated High Grade Pleomorphic Sarcoma- (Previously known as Storiform - Pleomorphic MFH) 

- Undifferentiated Pleomorphic Sarcoma with Giant Cells   (Previously known as Giant Cell MFH)

- Undifferentiated Pleomorphic Sarcoma with prominent Inflammation - (Previously known as Inflammatory MFH).

- Angiomatoid Fibrous Histiocytoma- (Angiomatoid Malignant Fibrous Histiocytoma) - This lesion will be discussed separately.

- Myxofibrosarcoma :

Visit: Pathology of Myxofibrosarcoma

 

Further reading:

- Malignant fibrous histiocytoma of soft tissue: an abandoned diagnosis.

-
Does malignant fibrous histiocytoma exist?

-Reassessment and clinicopathological prognostic factors of malignant fibrous histiocytoma of soft parts.

- Malignant fibrous histiocytoma: an analysis of 200 cases.

-Clinicopathologic re-evaluation of 100 malignant fibrous histiocytomas: prognostic relevance of subclassification.

-Discriminant analysis of prognostic factors for malignant fibrous histiocytoma in soft tissue

 

Undifferentiated High Grade Pleomorphic Sarcoma-

(Previously known as Storiform - Pleomorphic MFH) 

This variant probably embraces well defined sarcomas of various types with largely anaplastic features.

( Example - Pleomorphic leiomyosarcoma rhabdomyosarcoma liposarcoma). 

There are no reproducible histological criteria for the diagnosis of this tumour.

The tumour is usually located in the deep fascia or substance of the skeletal muscle of  the extremities and sometimes in the retroperitoneum.

Some of the tumours arise at the site of previous radiation therapy and at the site of surgical scar.

Macroscopically, these are large multinodular gray-white tumours.

These tumours share common histological features.

- Pleomorphic tumour cells
- Bizarre multinucleated cells
- Storiform pattern
- Inflammatory cells composed of lymphocytes, plasma cells, eosinophils, and xanthoma cells.
- Foci of metaplastic bone and cartilage.

Electron microscopic examination reveals that the tumour consists of a mixture of cells resembling fibroblasts, myofibroblasts, histiocytes and primitive mesenchymal cells.


Note: It has been observed that pleomorphic sarcomas with myogenic differentiation are  more likely to metastasize than the non-myogenic tumours.

Further reading:

- Malignant fibrous histiocytoma: pleomorphic sarcoma NOS or pleomorphic fibrosarcoma.

- Pleomorphic malignant fibrous histiocytoma: fact or fiction? A critical reappraisal based on 159 tumors diagnosed as pleomorphic sarcoma.  

-Myofibroblastic differentiation in malignant fibrous histiocytoma (pleomorphic myofibrosarcoma): a clinicopathological study.

 

Undifferentiated Pleomorphic Sarcoma with Giant Cells  

(Previously known as Giant Cell MFH) :      

Also termed 'Malignant giant cell tumour of soft parts.' 
 

Usually located in the  skeletal muscle of the extremities.

Superficial tumours (subcutis or fascia) have a better prognosis than deeply situated (subfascial) tumours.

Microscopic features:

- Multinodular tumour composed of fibroblasts, histiocytes and osteoclast like giant cells.
- Focal osteoid or bone formation present at the periphery.
- Stromal haemorrhage is present
- Cells display pleomorphism and mitotic figures
are conspicuous.
- When neoplastic osteoid and bone formation is prominent it is justifiable to call the lesion giant cell variant of soft tissue osteosarcoma.
- Leiomyosarcoma with osteoclast like giant cell is a subgroup of this variant.

Differential diagnosis:
Carcinoma (lung, thyroid pancreas);  other sarcomas with giant cells ; rarely melanoma.

Further reading

-Giant cell tumors of soft tissue: a clinicopathologic study of 18 benign and malignant tumors.

-Soft tissue giant cell tumor of low malignant potential: a proposal for the reclassification of malignant giant cell tumor of soft parts.

 

Undifferentiated Pleomorphic Sarcoma with prominent Inflammation -

(Previously known as Inflammatory MFH):

This rare variant is usually located in the retroperitoneum.

The tumour has a poor prognosis.

Microscopic features:

- A dense diffuse neutrophilic infiltrate unassociated with tissue necrosis, admixed with xanthoma cells  and  tumour cells.
-Phagocytosis of neutrophils by the tumour cells 
-Some tumour cells display bizarre atypical nuclei others have a more bland appearance.
-Focal storiform fibrous areas  
-Multinucleate or Reed Sternberg like cells may be present

Differential diagnosis:

Similar features are noted in:
Metastatic carcinoma from large bowel, lung or kidney ,in irradiated osteosarcoma, other sarcomas (Example:
Leiomyosarcoma), T-cell lymphoma , histiocytic lesions, xanthogranulomatous pyelonephritis.

Immunohistochemistry

Vimentin:( +)

alpha1-antitrypsin and alpha1antichymotrypsin: (+)

CD74: (++)

CD68: (+/-)

CD34, CD10 : may be positive in few cases

Desmin and actin: Negative

Cytokeratin, melanocytic markers are usually negative

 

Further reading

-Inflammatory malignant fibrous histiocytomas and dedifferentiated liposarcomas: histological review, genomic profile, and MDM2 and CDK4 status favour a single entity.

-
Inflammatory malignant fibrous histiocytoma: distinction from Hodgkin's disease and non-Hodgkin's lymphoma by a panel of leukocyte markers

- Inflammatory leiomyosarcoma: a morphological subgroup within the heterogeneous family of so-called inflammatory malignant fibrous histiocytoma. 

-Pleomorphic leiomyosarcoma: clinicopathologic and immunohistochemical study with special emphasis on its distinction from ordinary leiomyosarcoma and malignant fibrous histiocytoma. 

-Current topics in the diagnosis and treatment of malignant fibrous histiocytoma. 

 

 

 

 

Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)


 

 

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