Peripheral nerve sheath tumours (PNSTs) are tumours that arise from the protective layer of peripheral nerves. More specifically, they develop from nerve sheaths, which are layers of myelin and connective tissue that provide insulation to nerve fibres within the nervous system.
The nervous system is made up of two primary components: the central nervous system (CNS), and the peripheral nervous system (PNS). The CNS is made up of the brain and spinal cord, and is responsible for all sensory and motor functions in the body. The PNS encompasses all nerves outside of the CNS, and is responsible for all involuntary functions in the body. The PNS is further subdivided into the autonomic nervous system (ANS) and the somatic nervous system (SNS). The ANS controls involuntary processes and glands, such as heart rate, blood pressure, respiration, and digestion. Comparatively, the SNS is responsible for voluntary and involuntary muscle movements, as well as transmitting sensory information to the CNS.
This page will primarily focus on malignant (cancerous) peripheral nerve sheath tumours (MPNSTs). MPNSTs are less common than benign (non-cancerous) peripheral nerve sheath tumours (BPNSTs), and were previously referred to as neurofibrosarcomas. In rare cases, BPNSTs can undergo a malignant transformation when left untreated. For more information on BPNSTs, please refer to the Rare Cancers Australia Peripheral Nerve Sheath Tumours (Benign) page.
MPNSTs are generally diagnosed equally among the sexes, and tend to be diagnosed in people between the ages of 20-50. However, anyone can develop this disease.
Treatment
When cancers are detected, they are staged and graded based on size, metastasis (whether the cancer has spread to other parts of the body), and how the cancer cells look under the microscope. Staging and grading helps your doctors determine the best treatment for you.
Cancers can be staged using the TNM staging system:
- T (tumour) indicates the size and depth of the tumour.
- N (nodes) indicates whether the cancer has spread to nearby lymph nodes.
- M (metastasis) indicates whether the cancer has spread to other parts of the body.
This system can also be used in combination with a numerical value, from stage 0-IV:
- Stage 0: this stage describes cancer cells in the place of origin (or ‘in situ’) that have not spread to nearby tissue.
- Stage I: cancer cells have begun to spread to nearby tissue. It is not deeply embedded into nearby tissue and had not spread to lymph nodes. This stage is also known as early-stage cancer.
- Stage II: cancer cells have grown deeper into nearby tissue. Lymph nodes may or may not be affected. This is also known as localised cancer.
- Stage III: the cancer has become larger and has grown deeper into nearby tissue. Lymph nodes are generally affected at this stage. This is also known as localised cancer.
- Stage IV: the cancer has spread to other tissues and organs in the body. This is also known as advanced or metastatic cancer.
Cancers can also be graded based on the rate of growth and how likely they are to spread:
- Grade I: cancer cells present as slightly abnormal and are usually slow growing. This is also known as a low-grade tumour.
- Grade II: cancer cells present as abnormal and grow faster than grade-I tumours. This is also known as an intermediate-grade tumour.
- Grade III: cancer cells present as very abnormal and grow quickly. This is also known as a high-grade tumour.
Once your tumour has been staged and graded, your doctor may recommend genetic testing, which analyses your tumour DNA and can help determine which treatment has the greatest chance of success. They will then discuss the most appropriate treatment option for you.
Treatment is dependent on several factors, including location, age, stage of disease and overall health.
Treatment options for MPNSTs may include:
- Surgery to remove as much of the tumour as possible.
- Radiation therapy.
- Chemotherapy.
- Targeted therapy.
- Clinical trials.
- Palliative care.
For more information on the treatment options, please refer to the Rare Cancers Australia treatment options page.
Risk factors
While the cause of MPNSTs remains unknown, the following factors may increase the likelihood of developing the disease:
- Certain genetic mutations.
- Being diagnosed with certain genetic conditions, such as neurofibromatosis type 1 (NF1).
- Previous radiation therapy treatment.
- Being diagnosed with a BPNST.
Not everyone with these risk factors will develop the disease, and some people who have the disease may have none of these risk factors. See your general practitioner (GP) if you are concerned.
Early symptoms
Some patients with MPNSTs may appear asymptomatic in the early stages of disease. As the tumour grows, symptoms may appear, and often vary based on location. Some of these symptoms include:
- Pain in the affected area.
- Numbness and/or tingling in affected area.
- Weakness and/or loss of function in affected area.
- A mass that may be firm and/or palpable.
Not everyone with the symptoms above will have cancer, but see your general practitioner (GP) if you are concerned.
Diagnosis/diagnosing
If your doctor suspects you have a MPNST, they may order the following tests to confirm the diagnosis and refer you to a specialist for treatment.
Physical examination
Your doctor will collect your overall medical history, as well as your current symptoms. Following this, they may examine your body to check for any abnormalities.
Neurological examination
A neurological examination assesses sensory and motor functions, and can generally be done in your GPs office. The doctor may check your vision, hearing, balance, coordination, strength, and reflexes, depending on the signs and symptoms you have described. Any problem that is detected in this exam can help determine which portion of the CNS needs further investigation.
Imaging & Blood tests
The doctor will take images of your body using magnetic resonance imaging (MRI), a computed tomography scan (CT scan), x-rays, bone scan and/or positron emission tomography (PET scan), depending on where it is suspected the cancer is. The doctor may also look at other parts of the body and look for signs of metastasis. Additionally, a blood test may be taken to assess your overall health and help guide treatment decisions.
Electromyogram (EMG)
An electromyogram is a diagnostic procedure used to measure the response of nerves and skeletal muscles to electrical activity. For this test, small needles are inserted into your muscle and records the electrical activity in the muscle as you try to move it. This procedure is often performed by a specialist, and is often performed while you are awake.
Nerve Conduction Study
A nerve conduction study, also known as a nerve conduction velocity test, is a diagnostic procedure used to measure the speed of electrical impulses through a nerve. The test involves stimulating the nerves via small electrode patches on the skin with a very small electrical impulse. Nerve conduction studies are often performed alongside an EMG.
Biopsy
Once the location of the cancer has been identified, the doctor will perform a biopsy to remove a section of tissue using a needle. This tissue will then be sent to the lab and analysed for cancer cells.
Prognosis (Certain factors affect the prognosis and treatment options)
While it is not possible to predict the exact course of the disease, your doctor may be able to give you a general idea based on the rate and depth of tumour growth, susceptibility to treatment, age, overall fitness, and medical history. Generally, BPNSTs have a good prognosis and survival rates. However, if the tumour has become a MPNST, the prognosis may not be as good, and there may be a higher risk of recurrence. It is very important to discuss your individual circumstances with your doctor to better understand your prognosis.
References
Some references are to overseas websites. There may be references to drugs and clinical trials that are not available here in Australia.