What Is a Malignant Peripheral Nerve Sheath Tumor (MPNST)?
A malignant peripheral nerve sheath tumor is a rare, aggressive soft tissue sarcoma that develops in protective coverings called sheaths surrounding certain nerves. These nerves are part of the peripheral nervous system—the nervous system outside of the brain and spine.
MPNST affects both children and adults and is often connected to a genetic syndrome called neurofibromatosis type 1 (NF1). These cancerous tumors are found most often in the arms and legs, but can form anywhere in the body. Other locations include the head, neck, chest, abdomen (belly), pelvis, and back.
Malignant peripheral nerve sheath tumors used to be called neurogenic sarcoma (sarcoma of the nervous system), neurofibrosarcoma, malignant neurofibroma, and malignant schwannoma. They are now collectively referred to as malignant peripheral nerve sheath tumors to include all the various places they can start.
While most cases of MPNST occur in adults ages 20 to 50, the cancer can also develop in older children and teens. These tumors can grow quickly and invade nearby tissues such as blood vessels and lymph vessels. They also frequently return after treatment and metastasize (spread), most often to the lungs.
MPNST is rare, with a little more than 200 cases diagnosed in the U.S. each year. The cancers represent just 3 percent of soft tissue sarcomas.
The Sarcoma Program at Penn Medicine’s Abramson Cancer Center has extensive experience caring for malignant peripheral nerve sheath tumors. We perform sophisticated surgeries, including those that spare arms and legs affected by the tumors. Our nationally recognized experts also work closely with the Sarcoma Program at the Children’s Hospital of Philadelphia.
Nerve Sheath Tumor Symptoms
Nerve sheath cancers often go unnoticed in early stages, as small tumors don’t usually cause symptoms. However, as tumors grow, you may experience:
- Differences in nerve function, such as weakness in a particular area or changes to sense of touch, temperature, or pain
- Noticeable lump
- Pain or tingling in the affected area
What Causes Nerve Cancer?
Researchers don’t yet understand exactly why most cancerous nerve sheath tumors form. Some known factors can increase your risk of developing one:
- Genetics: Genetic changes can lead to syndromes that raise the risk of developing certain health conditions, including cancer. While these changes are often inherited from parents, some happen on their own during development in the womb. A genetic syndrome called neurofibromatosis type 1 (NF1) leads to tumors developing in nerve sheaths. These tumors are often noncancerous, but about 10 percent of people with NF1 develop a cancerous nerve sheath tumor, and NF1 is connected to up to 50 percent of MPNST cases.
- Other tumors: In some instances, a noncancerous neurofibroma can turn cancerous. In very rare cases, noncancerous benign schwannomas can also turn malignant.
- Previous radiation therapy: Receiving radiation therapy can increase the risk of developing MPNST years later. This risk rises in people with NF1, as the syndrome appears to make people more sensitive to radiation side effects.
Diagnosing Nerve Sheath Tumors
At Penn, evaluations for malignant peripheral nerve sheath tumors start with an exam of the affected area and asking about symptoms. One of our doctors will also conduct a specialized neurological exam to see if the tumor affects any of your body functions. If NF1 is suspected, we may recommend undergoing genetic testing.
Scans can then provide more information about the tumor, including its size and location. Testing usually starts with magnetic resonance imaging (MRI). We may also turn to a scan that combines positron emission tomography (PET) with computed tomography (CT) if you have NF1 and we want to review all of the masses at the same time.
If an MPNST is suspected, one of our doctors will likely perform an image-guided needle biopsy to take a sample of tumor tissue. The tissue is sent to our specialized pathologists to study under a microscope and put through several lab tests.
Together, the exams, scans, and biopsy results help our team stage the cancer and plan treatment for the most effective recommendations. Learn more about sarcoma diagnosis and staging.
Treating Malignant Peripheral Nerve Sheath Tumors
MPNST treatment at Penn focuses on removing the tumor when possible. As with sarcoma surgery for other tumor types, the best results come from taking MPNST out in one piece, along with a buffer of healthy tissue. This likelihood also depends on tumor size and location.
When considering surgical removal of tumors involving nerves, our doctors determine what impact treatment might have on certain body functions. They will discuss possible side effects with you before agreeing together on a plan.
To reduce the risk that cancer returns, our team may recommend adding radiation therapy either before or after surgery.
Our team may recommend chemotherapy when the tumor has spread to more than one area or if surgery is not initially possible due to large size or location. A sarcoma clinical trial may provide options for cancer that returns or spreads.
Learn more about sarcoma treatment at Penn Medicine, including limb-sparing operations and procedures to transfer nerves during reconstructive surgeries.
Make an Appointment
Please call 800-789-7366 or make an appointment.
The Penn Sarcoma Program offers same-day appointments to patients who have their imaging available. To learn more, call 215-349-8200.