Undifferentiated Pleomorphic Sarcoma

Undifferentiated pleomorphic sarcoma (UPS) is a type of soft tissue cancer (sarcoma). Soft tissues connect and support your body. They include:

• Blood vessels.
• Fat.
• Fibrous tissues, including tendons, ligaments and cartilage.
• Muscles.
• Nerves.
• Skin.

This type of sarcoma usually affects soft tissues but can also happen in bones, where it behaves similar to other types of more common sarcomas that originate in bone (osteosarcoma).

UPS most often occurs in your legs and arms. Less often, it develops in the back part of your abdomen called the retroperitoneum. It’s generally an aggressive, malignant cancer that spreads to other parts of your body about 40% of the time. The most common location it spreads to is your lungs, and less commonly to your lymph nodes. Because of its aggressive nature, there’s a potential for this cancer to come back in the same site where it was previously removed (local recurrence).

Is undifferentiated pleomorphic sarcoma the same as malignant fibrous histiocytoma?

Malignant fibrous histiocytoma is the original name for this condition. Scientists used this name because they thought it originated from special immune cells called histiocytes. But later research showed stem cells called mesenchymal cells are likely the origin rather than histiocytes.

In 2002, the World Health Organization (WHO) replaced malignant fibrous histiocytoma with the term undifferentiated pleomorphic sarcoma. While some people and healthcare providers still use the old name, it’s more common to refer to this condition as an undifferentiated pleomorphic sarcoma. Despite the name differences, how the cancer behaves remains the same.

How common is soft tissue sarcoma?

Overall, soft tissue sarcoma is rare. A recent estimate from the American Cancer Society suggests that about 13,000 people develop soft tissue sarcoma each year. That’s less than 1% of all cancers diagnosed in adults. Within adults that have a diagnosis of soft tissue sarcoma, UPS is the most common variant.