Overview
Undifferentiated pleomorphic sarcoma (UPS) is a rare type of cancer called sarcoma. It used to be known as malignant fibrous histiocytoma.
UPS most often develops in the soft tissues that connect, support and surround other body structures. Soft tissues include muscle, fat, blood vessels, nerves, tendons and the linings of joints. Rarely, UPS can start in bone. UPS of bone is considered a bone sarcoma and is treated differently from soft tissue UPS.
Undifferentiated pleomorphic sarcoma most often forms in a leg or an arm. Less often, it can happen in the area behind the organs in the belly called the retroperitoneum.
This cancer gets its name from the way the cancer cells look under a microscope. Undifferentiated means the cells don't look like the healthy cells around them. Pleomorphic (plee-o-MOR-fik) means the cells grow in many shapes and sizes.
Treatment for UPS depends on where the cancer is located and whether it has spread. Treatment often involves surgery, radiation therapy and medicines.
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Symptoms
Symptoms of undifferentiated pleomorphic sarcoma (UPS) depend on where the cancer is located. It most often forms in a leg or an arm. But it can happen anywhere in the body.
Signs and symptoms may include:
- A growing lump or area of swelling.
- A feeling of pain or pressure.
UPS symptoms can be different if the cancer has spread to other parts of the body. When cancer spreads, it's called metastatic cancer. UPS that has spread most often spreads to the lungs. If the cancer has spread to the lungs, symptoms may include shortness of breath, a cough or chest pain.
When to see a doctor
Make an appointment with a doctor or other healthcare professional if you have ongoing symptoms that worry you.
Causes
The exact cause of undifferentiated pleomorphic sarcoma isn't known.
Cancer happens when cells get changes in their DNA. A cell's DNA holds the instructions that tell the cell what to do. In healthy cells, the DNA gives instructions that help control when cells grow, multiply and die.
In cancer cells, the DNA changes give different instructions. The changes tell the cancer cells to grow and multiply quickly. Cancer cells can keep living when healthy cells would die. This causes cancer cells to build up.
The cancer cells might form a mass called a tumor. The tumor can grow to invade and destroy healthy body tissue. In time, cancer cells can break away and spread to other parts of the body, which is called metastasis.
Risk factors
Factors that may raise the risk of undifferentiated pleomorphic sarcoma include:
- Older age. This cancer is most common in people 50 to 70 years old, but it can happen at any age. UPS in children is rare.
- Previous radiation therapy. Rarely, this cancer can form in an area of the body that was previously treated with radiation therapy.
Most people who develop undifferentiated pleomorphic sarcoma have no known risk factors. Many people who have risk factors never develop this cancer.
Sept. 05, 2026