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 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, bones, and liver. In the extremities, it presents as a painless enlarging soft tissue mass. There is a case report of human-human transmission, in a surgeon that injured their hand while working on a PUS case. A surgeon cut his hand while resecting a tumor and seeded the patient's cancer cells on his hand.
