Undifferentiated pleomorphic sarcoma of bone, formerly known as malignant fibrous histiocytoma of bone, is a rare and aggressive type of bone cancer characterized by the presence of undifferentiated malignant cells that exhibit pleomorphic features. These tumors can occur in any bone but are more commonly found in the long bones, such as the femur and tibia. The condition often presents with pain, swelling, and reduced mobility in the affected area.