Malignant fibrous histiocytoma, MFH

Definition

The diagnosis of MFH was at one time extremely popular, constituting 40% of adult mesenchymal malignancies. However, it has now become clear that the morphological patterns seen in MFH are shared buy a range of poorly differentiated malignant neoplasms which can now be accurately subclassified. The latest WHO classification regards MFH as a synonym for pleomorphic sarcoma.

Histopathology

The tumour cells are pleomorphic. They may be large with copious cytoplasm, pale to eosinophilic, sometimes vacuolated. Cells may be oval or spindled, but not greatly elongated. Nuclei are bizarre, often multilobated. The nuclear membrane tends to be jagged.

Subtypes and their reclassification

Below are the subtypes of MFH as they were recognised and the current diagnostic entities that need to be considered.

• superficial MFH = Atypical fibroxanthoma

• Storiform / pleomorphic. This was the most common type and the archetypal MFH. These now equate to undifferentiated pleomorphic sarcoma, which is a diagnosis of exclusion when ancillary methods fail to demonstrate a specific line of differentiation.

• Myxoid = myxofibrosarcoma

• Giant cell: these are now recognised to be a heterogeneous group of tumours, including leiomyosarcoma with osteoclastic giant cells, giant cell tumour of soft tissues and extraskeletal osteosarcoma.

• Inflammatory: these are now considered a heterogeneous group of unrelated lesions, including lymphomas, leiomyosarcomas and sarcomatoid carcinomas. Those cases with chromosomal rearrangement at 12q13-14 and MDM2/CDK4 amplification2 are dedifferentiated liposarcomas with the inflammatory component masking the adipocytic cells. A careful search needs to be made for a well differentiated liposarcomatous component.

• Angiomatoid: this variant occurs in younger patients and has a low metastatic rate of about 2%, usually to regional lymph nodes. There is positivity for desmin in 40% of cases and for EMA in 40% of cases.

Differential diagnosis

It is important to differentiate sarcomas from pleomorphic carcinomas, melanomas and lymphomas.

• Extraskeletal osteosarcoma

• Malignant peripheral nerve sheath tumour

Tumours with a relatively good prognosis:

• dedifferentiated liposarcoma

• atypical fibroxanthoma

Benign tumours showing nuclear pleomorphism:

• symplastic leiomyoma

• pleomorphic hyalinising angiectatic tumour

Prognosis

Pleomorphic sarcomas with myoid differentiation (pleomorphic leiomyosarcoma and pleomorphic rhabdomyosarcoma) are associated with a particularly poor prognosis.

References

1 Tos AP Classification of pleomorphic sarcomas: where are we now? Histopathology 2006; 48:51-62

2 Coindre JM, Hostein I, Maire G, et al. Inflammatory malignant fibrous histiocytomas and dedifferentiated liposarcomas: histological review, genomic profile, and MDM2 and CDK4 status favour a single entity. J Pathol 2004; 203:822-30

This page last revised 12.1.2008.

©SMUHT/PW Bishop