Causes

It's not clear what causes undifferentiated pleomorphic sarcoma.

Doctors know this cancer begins when a cell develops changes in its DNA. A cell's DNA contains the instructions that tell a cell what to do. The changes tell the cell to multiply rapidly, creating a mass of abnormal cells (tumor). The cells can invade and destroy nearby healthy tissue. In time, the cancer cells can break away and spread (metastasize) to other parts of the body, such as the lungs and bones.