A malignant peripheral nerve sheath tumour (MPNST) is a type of cancer called a soft tissue sarcoma. Soft tissue sarcomas are cancers that develop in the supporting or connective tissues of the body (such as muscle, fat, nerves and blood vessels).
MPNSTs probably start from Schwann cells, which form the protective sheath around nerves. People in their 20s to 50s are most likely to be affected. Occasionally children can develop MPNSTs but this is rare.
It is not known what causes these tumours. People who have an inherited condition called neurofibromatosis type 1 (NF1) have an increased risk of developing MPNST. About half of MPNSTs are found in people with NF1.
In NF1 non-cancerous tumours of the nerve sheath cells can develop in the nerves just under the skin or deeper in the body. These form lumps called plexiform neurofibromas. In about 2 to 5 out of 100 (2-5%) of people with NF1, a neurofibroma becomes cancerous - a MPNST. Signs of this change can be the swelling beginning to grow or becoming painful.
MPNSTs are most likely to occur in the arms close to the shoulders, the legs close to the buttock or the trunk (the part of the body between the neck and bottom). But they can occur in any part of the body.
The first sign of a MPNST is often a lump or mass that is growing in size. Sometimes a person will have this for weeks or months before other symptoms develop. The symptoms of MPNSTs depend on where the growth is in the body. They can include
- Pain
- Altered sensations such as numbness, burning, “pins and needles”
- Weakness in the affected area
Tests to diagnose MPNSTs may include imaging tests such as X-rays and scans (MRI, CT or PET). A sample of tissue (biopsy) will also be taken from the tumour and looked at under the microscope.
These tests also help the doctors to plan treatment. They will show the size of the tumour and if it has spread. If the cancer does spread it is most often found in the lungs but other places are also possible.
Treatment for MPNSTs is usually carried out in a cancer centre with doctors specialising in the treatment of sarcomas. Treatment depends on a number of factors including a person's age and general health, the size of the tumour, where it is, and how slowly or quickly it is growing (grade).
The main treatment is surgery to remove the tumour. Removing all of the tumour with a margin of healthy tissue around it offers the best chance of cure. If a tumour is large, or attached to surrounding tissues in the body, radiotherapy or chemotherapy may be given to try to shrink the sarcoma, so that an operation is possible.
Sometimes surgery is followed by a course of radiotherapy. This is given to reduce the chance of the cancer coming back. Radiotherapy may also be used if a MPNST is in a part of the body where surgery isn't possible or might be dangerous. Chemotherapy may be given as part of the overall treatment.