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 tissuea group of cells that work together to perform a function 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, bloodthe red bodily fluid that transports oxygen and other nutrients around the body 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 malignantcancerous, may grow and spread to other areas of the body peripheral nerve sheath tumours (MPNSTs). MPNSTs are less common than benignnot cancerous, can grow but will not spread to other body parts 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.
Variants of MPNSTs
There are several different variants of MPNST, which are categorised based on the types of cellsthe basic structural and functional unit of all living things they develop from.
Malignant Melanotic Nerve Sheath Tumour (MMNST)
Malignant melanotic nerve sheath tumours (MMNSTs), also known as melanotic schwannomas, are a rare variant of MPNST that develop from Schwann cells in the peripheral nervous system and melanocytes. Unlike most MPNSTs, MMNSTs are generally not associated with neurofibromatosis, and are associated with Carney complex. MMNSTs have a predilection for spinal and visceral nerves in the body, can be aggressive, and may not have as good of a prognosisto predict how a disease/condition may progress and what the outcome might be as other types of MPNSTs.
Rare types of MPNST
These types of MPNST are considered rare:
- Epithelioid MPNST.
- MPNST with divergent differentiation.
- MPNST with perineural differentiation.
- MPNST with heterologous rhabdomyoblastic differentiation.
Treatment
When cancers are detected, they are staged and graded based on size, metastasiswhen the cancer has spread to other parts of the body, also known as mets, and how the cancera disease where abnormal cells split without control and spread to other nearby body tissue and/or organs cells look under the microscope. Stagingthe process of determining how big the cancer is, where it started and if it has spread to other areas and grading helps your doctors determine the best treatment for you.
Cancers can be staged using the TNM staging system:
- T (tumoura tissue mass that forms from groups of unhealthy cells) indicates the size and depth of the tumour.
- N (nodea small lump or mass of tissue in your body) indicates whether the cancer has spread to nearby lymph nodessmall bean-shaped structures that filters harmful substances from lymph fluid.
- 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 localisedaffecting only one area of body 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 advancedat a late stage, far along or metastatic cancer.
Cancers can also be graded based on the rate of growth and how likely they are to spread:
- Gradea description of how abnormal cancer cells and tissue look under a microscope when compared to healthy cells 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 testinga procedure that analyses DNA to identify changes in genes, chromosomes and proteins, which can be used to analyse tumour DNA to help determine which treatment has the greatest chance of success, 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:
- Surgerytreatment involving removal of cancerous tissue and/or tumours and a margin of healthy tissue around it to reduce recurrence to remove as much of the tumour as possible.
- Radiation therapya treatment that uses controlled doses of radiation to damage or kill cancer cells.
- Chemotherapya cancer treatment that uses drugs to kill or slow the growth of cancer cells, while minimising damage to healthy cells.
- Targeted therapymedication that targets specific molecular features of cancer cells.
- Clinical trialsresearch studies performed to test new treatments, tests or procedures and evaluate their effectiveness on various diseases.
- Palliative carea variety of practices and exercises used to provide pain relief and improve quality of life without curing the disease.
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 riskthe possibility that something bad will happen 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.
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 massa growth of cells that come together to make a lump, may or may not be cancer 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
If your doctor suspects you have a MPNST, they may order the following tests to confirm the diagnosisthe process of identifying a disease based on signs and symptoms, patient history and medical test results and refer you to a specialist for treatment:
- Physical examinationan examination of your current symptoms, affected area(s) and overall medical history.
- Neurological examinationan assessment of sensory and motor functions, such as vision, balance and coordination.
- Imagingtests that create detailed images of areas inside the body tests, potentially including:
- CT (computed tomography) scana type of medical imaging that uses x-rays and computer technology to create detailed images of the body.
- MRI (magnetic resonance imaging)a type of medical imaging that uses radiowaves, a strong magnet and computer technology to create detailed images of the body.
- PET (positron emission tomography) scana type of medical imaging that uses radioactive tracers to create detailed images of the body.
- Ultrasounda type of medical imaging that uses soundwaves to create detailed images of the body .
- Blood teststesting done to measure the levels of certain substances in the blood.
- Electromyogram (EMG)a diagnostic procedure used to measure the response of nerves and skeletal muscles to electrical activity.
- Nerve conduction studiesa diagnostic procedure used to measure the speed of electrical impulses through a nerve.
- Biopsyremoval of a section of tissue to analyse for cancer cells.
