Malignant fibrous histiocytoma

Pleomorphic undifferentiated sarcoma
Micrograph of a pleomorphic undifferentiated sarcoma. H&E stain.
Classification and external resources
Specialty	Oncology
ICD-10	C49 (ILDS C49.M10)
DiseasesDB	31471
eMedicine	radio/420
MeSH	D051677
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Pleomorphic undifferentiated sarcoma (abbreviated PUS), also undifferentiated pleomorphic sarcoma and previously malignant fibrous histiocytoma (abbreviated MFH), is a type of soft tissue sarcoma.

It is considered a diagnosis of exclusion for sarcomas that cannot be more precisely categorized.

PUS is regarded as the most common soft tissue sarcoma of late adult life. It rarely occurs in children. It occurs more often in Caucasians than in those of African or Asian descent and is a male-predominant disease, afflicting two males for every female.

PUS occurs most commonly in the extremities and retroperitoneum, but has been reported in other sites. Metastasis occurs most frequently in the lungs (90%), bones (8%), and liver (1%).

In the extremities, it presents itself as a painless enlarging soft tissue mass.

It can be detected by magnetic resonance imaging (MRI), but a biopsy is required for the definitive diagnosis. MRI findings typically show a well-circumscribed mass that is dark on T1-weighted images and bright on T2-weighted images. Central necrosis is often present and identifiable by imaging, especially in larger masses.

Pleomorphic undifferentiated sarcomas are, by definition, undifferentiated, meaning (as the name implies) that they do not bear a resemblance to any normal tissue.

The histomorphology, otherwise, is characterized by high cellularity, marked nuclear pleomorphism, usually accompanied by abundant mitotic activity (including atypical mitoses), and a spindle cell morphology. Necrosis is common and characteristic of high grade lesions.

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