Undifferentiated pleomorphic sarcoma, previously malignant fibrous histiocytoma, is a type of cancer, namely a soft-tissue sarcoma.. It is considered a diagnosis of exclusion for sarcomas that cannot be more precisely categorized. Other sarcomas are cancers that form in bone and soft tissues, including muscle, fat, blood vessels, lymph vessels, and fibrous tissue (such as tendons and ligaments).

https://en.wikipedia.org/wiki/Malignant_fibrous_histiocytoma