Undifferentiated pleomorphic sarcoma (previously known as malignant fibrous histiocytoma) is a type of soft tissue cancer. It’s a rare cancer that often spreads to other parts of your body and comes back after treatment. Early detection and treatment offer the best prognosis.
Undifferentiated pleomorphic sarcoma (UPS) is a type of soft tissue cancer (sarcoma). Soft tissues connect and support your body. They include:
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).
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
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.
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.
Scientists aren’t exactly sure how this malignant soft tissue sarcoma forms. Genetic changes are a likely cause. Radiation therapy, when used to treat other types of cancer that were previously found in the same location, is also linked to this condition — though, this is very rare. A radiation-associated sarcoma usually forms near the area previously treated with radiation, generally seven to 20 years after radiation therapy was completed. The risk of a radiation-associated sarcoma is quite low (less than 0.5%), though these radiation-associated sarcomas can account for up to 5% of all soft tissue sarcomas.
Often, tumors don’t cause any symptoms and grow for a long time before people notice them. In your arms and legs, you may notice a lump or experience pain if the tumor presses on a nearby nerve or causes a “pressure” sensation in the surrounding muscle. In one study, the average tumor size at diagnosis was 9 centimeters, about the width of a credit card.
If the tumor affects a bone, it can cause:
Tumors in the back of your abdomen can cause:
Your healthcare provider reviews your medical history and performs a physical exam. An MRI (magnetic resonance imaging), for your arms and legs, or a CT scan (computerized tomography), for your abdominal areas, are the main radiology tests healthcare providers use to determine tumor size and involvement of your blood vessels and nerves.
A biopsy, which is the collection of a sample of your tissue for examination under a microscope, also helps your healthcare provider make an accurate diagnosis. Examination of the cell structure of the tumor (histology) is the primary method for identifying the type of soft tissue cancer. Despite a common misconception, a biopsy doesn’t “spread” tumor cells.
A CT scan can also help your healthcare provider assess whether the cancer has spread to other areas like your lungs.
Your healthcare provider uses information about the tumor size, the types of cells it contains and whether it has spread to determine the stage of cancer. Staging helps your healthcare provider recommend the best treatment options and determine your prognosis.
The standard treatment is surgical removal of the entire tumor with a “normal tissue” cuff (called a margin) around it. Healthcare providers perform limb-sparing surgery as often as possible to help you maintain function in your arms and legs. Amputation is rare.
Along with surgery, healthcare providers usually recommend radiation therapy. This powerful combination allows for the best chance of preventing the sarcoma from coming back in the same area. Your healthcare provider might administer radiation either before or after surgery. If you have more advanced cancer or your cancer has spread to multiple locations, you may receive chemotherapy.
Follow-up monitoring is essential for detecting recurrent tumors (tumors that come back) or the spread of cancer to other parts of your body. Your healthcare provider will schedule appointments every three to six months for the first two years. After that, checkups will be spaced out every six to 12 months, and generally, follow-up lasts at least 10 years. But more advanced tumors will require follow-up care more frequently.
As healthcare providers aren’t sure what causes this condition, there aren’t any strategies for preventing it.
Overall survival rates five years after diagnosis are about 60%. As with all forms of cancer, early detection leads to better outcomes. Tumors that are bigger than 10 centimeters, grow deep in the muscle and are high grade (the most aggressive form) have the highest risk for cancer spread.
As stated, your individual prognosis depends on factors related to your age, tumor characteristics, treatment and whether the disease has spread. Factors that indicate a poorer prognosis include:
After treatment, your healthcare provider will monitor you closely for recurrent tumors and the spread to other parts of your body. Attend all follow-up appointments and let your healthcare provider know if you experience any unusual symptoms.
A note from Cleveland Clinic
Undifferentiated pleomorphic sarcoma (UPS) is a rare type of cancer that happens in soft tissues. It’s treatable, but can be aggressive and recurrent. Healthcare providers aren’t sure what causes it, but previous radiation therapy seems to be a factor in some cases. If you’ve had radiation therapy, talk to your healthcare provider about your risk and be vigilant about symptoms. Early detection and treatment gives you the best chance at eliminating this cancer for good.
Last reviewed by a Cleveland Clinic medical professional on 02/21/2022.
Learn more about our editorial process.
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy