What is a germ cell tumour?
Germ cell tumours are thought to develop from primordial germ cells. These are a type of stem cell in an embryo that has begun to form into either sperm or eggs, and will develop further after the child has been born and then reached puberty. These cells can start to grow in an abnormal way, giving rise to germ cell tumours that usually occur in the testis or ovary, referred to as ‘gonadal’ germ cell tumours.
Unfortunately, rather than gathering in the testicle or ovary as they should do, some germ cells can be left behind in other parts of the body, such as the mediastinum (chest), retroperitoneum (abdomen) and the central nervous system or CNS (brain or spinal cord). Therefore germ cells tumours can also occur at these sites and are referred to as ‘extragonadal’ (meaning outside of testes or ovaries) germ cell tumours.
Germ cell tumours in the CNS
Germ cell tumours mainly occur in children during puberty (10-19 years) and account for approximately 4% of brain tumours in children. They occur less frequently in adults and the combined incidence (in children and adults) is less than 1% of all brain tumours in the Western World (Northern America and Europe). For reasons yet to be established, they are much more common (up to 15% of brain tumours) among the East Asian population (highest reported in Japan).
Germ cells tumours tend to occur in the midline location. The most common site for CNS germ cell tumours is the pineal region, followed by the pituitary gland region, although they can arise in other areas of the central nervous system such as ventricles, basal ganglia and thalamus.
What are the types of germ cell tumours in the CNS?
Based on the histolopathology (tumour features as seen under a microscope), immunohistochemistry (their protein type expression) and genetic make up, germ cell tumours are classified into different tumour types as per the World Health Organisation (WHO) classification of CNS tumours. The most common CNS germ cell tumour is the germinoma. The other germ cell tumours, broadly referred to as non-geminomatous germ cell tumours are embryonal carcinoma, yolk sac tumour, choriocarcinoma and teratomas. When there is mixed occurrence of two or more of the above tumours, it is called a mixed germ cell tumour.
Germinomas are the most commonly diagnosed form of CNS germ cell tumour. They usually occur in the pineal and pituitary regions of the brain, although they can form in other parts of the CNS.
Germinomas tend to cause small increases in total HCG and may also show increased levels of an enzyme usually produced by the placenta during pregnancy, called placental alkaline phosphatase (PLAP).
- Around 80% of all intracranial germ cell tumours are classified as pineal germinonas.
- Pineal germinomas account for approximately 50% of all tumours found in the pineal region of the brain, which surrounds the pineal gland.
- Pineal germinomas are more common in males than females, the ratio being approximately 13 males for every 1 female.
- Most patients are diagnosed at under 20 years old
Discover more about the pineal region on our Pineal Region Tumours page.
Non-germinomatous germ cell tumours (NGGCTs)
Non-germinomatous germ cell tumours (NGGCTs) are a group that represents approximately one third of all germ cell tumours. Types of NGGCTs in the CNS include the following:
These are named after the appearance of the tumour cells, which resemble embryonic germ discs. Pure embryonal carcinomas are not known to secrete any tumour markers. However, they tend to occur mixed with other germ cell tumour subtypes (see below), especially yolk sac tumours, so these other tumour cells may secrete AFP or beta-hCG.
Yolk sac tumour: endodermal sinus tumour
Yolk sac tumours are so called because the tumour cells resemble primitive (embryonal) yolk sac. They release the hormone alfa-foetoprotein (AFP) and can occur as a mixed germ cell tumour in combination with other germ cell tumours.
Choriocarcinoma in the brain
Choriocarcinomas release the hormone beta-human chorionic gonadotrophin (beta-hCG) and hence the name. Similar to embryonal and yolk sac tumours, choriocarcinomas can also occur in combination as a mixed germ cell tumour.
Central nervous system (CNS) teratomas are described as mature or immature depending upon their histology (how their cells look under a microscope).
Unlike other CNS germ cell tumours, teratomas in the brain do not secrete enzymes or hormones in amounts that can be reliably used as tumour markers.
Mature teratomas look very similar to healthy cells but are made of different kinds of human body tissue that should not be found within the CNS such as skin, hair, muscle, and bone.
Immature teratomas are made of cells that look like those found within a foetus in the womb. Some immature teratomas may contain a mixture of mature and immature cells, in varying proportions.
Teratoma with malignant transformation
Unfortunately, some teratomas become more aggressive in their growth, so these would be classified as having undergone malignant transformation.
Are CNS germ cell tumours (GCTs) benign or cancerous?
This depends upon the stage (extent of tumour spread) and type of the tumour.
Patients with a tumour confined to one part of the brain and with no traces of tumour markers in the CSF are classified as metastatic negative (M0), meaning that the tumour has not spread and hence will be easier to treat. If they are easy to remove, they could be considered benign.
Patients who have raised tumour markers in the CSF and/or tumours in more than one area of the brain and spinal cord are considered to be metastatic positive (M+). Unfortunately, this means that the tumour has spread (metastasised) and the disease is therefore more difficult to treat. Unfortunately, such tumours are considered to be cancer.
What is the prognosis for a germ cell tumour in the brain?
The prognosis for an intracranial germ cell tumour varies. This is largely dependent on:
- Type and position of the tumour
- Type and level of tumour markers
- Whether or not it has spread (metastasised) by the time it has been diagnosed
- Whether or not it is newly diagnosed or has recurred after treatment.
An exact prognosis is not available for every type of germ cell tumour due to their rarity, so each patient is regarded as an individual, and treatment is personalised to reflect their unique situation.
80%-90% of patients with germinomas can be cured by radiotherapy alone, whilst some also require chemotherapy. Non-germinomatous germ cell tumours have a 40%-85% cure rate, depending to some extent on how far they have spread by the time they are diagnosed.
Mature teratomas may be curable by surgery alone.
Mixed germ cell brain tumours are more challenging to treat because they contain a mixture of different types of cancerous cells, so these might be treated by a combination of surgery, radiotherapy and chemotherapy, for example.
Teratoma prognosis depends on the type of cells within the tumour. In general, mature teratomas are considered to be relatively benign and may be able to be removed using surgery alone, whereas immature teratomas are much more difficult to treat, with survival rates of 50-70%.
What are the symptoms of germ cell tumours?
Signs and symptoms of germ cell tumours depend upon where the tumour has developed.
If they are in the pineal region, symptoms may include:
- Nausea and vomiting
- Poor balance, for example whilst walking
- Uncoordinated body movements (ataxia)
- Poor co-ordination
- Disruption of sleep patterns
- Memory issues
- Early puberty in children
- Upward gaze of the eyes, a condition known as Parinaud syndrome.
If the tumour is affecting the pituitary gland, symptoms may include:
- Delayed or early puberty
- Stunted growth
- Changes in eyesight such as loss of peripheral vision
- Diabetes type 2, symptoms of which include frequent urination and extreme thirst
How is a CNS germ cell tumour diagnosed?
The most reliable way to diagnose any kind of brain tumour is initially by an MRI scan and then by taking a biopsy (a small sample of the tumour, removed during neurosurgery) for analysis in a laboratory.
For germ cell tumours, a sample of blood and/or cerebral spinal fluid (CSF) will also be taken. The sample would then be analysed in a laboratory because raised levels of an enzyme called placental alkaline phosphatase (PLAP) or hormones called called alpha-fetoprotein (AFP) and beta-human chorionic gonadotropin (beta-hCG) help to clarify which type of germ cell tumour is present.
Do germ cell tumours occur due to genetic problems?
Germ cell tumours occur sporadically (meaning without prior or inherited genetic abnormality). However there is an increased risk of these tumours in Klinefelter syndrome (47 XXY), which is a chromosomal abnormality with an additional X chromosome. Other syndromes associated are Down’s syndrome and Neurofibromatosis type I (NF1).
Treatment options for germ cell tumours
The first line of treatment for certain germ cell tumours, particularly teratomas, may be surgery. This will depend on the location of the tumour and the related risk of side effects.
Germinomas are likely to be treated with radiotherapy alone, as this can cure 80-90% patients with no further treatment required.
Chemotherapy is also likely to be offered for patients with germ cell tumours, particularly those that are non-germinomatous.
Some patients with aggressive germ cell tumours may be offered high-dose chemotherapy with stem cell rescue. The first step in such treatment is to remove stem cells that are immature blood cells from the blood or bone marrow of the patient, which are then frozen and stored. The patient is then given high doses of chemotherapy to kill as many of the cancer cells as possible. Afterwards, the stem cells are thawed and returned to the patient via a blood transfusion, so that they can quickly restore the levels of healthy blood cells.
New treatments may be available to some patients in the context of clinical trials. These may include immunotherapy, novel combinations of existing chemotherapy drugs, and emerging drugs that target the specific genetic mutations of individual tumour types.
How will we find a cure for CNS germ cell tumours?
Research we are funding across all of our dedicated Research Centres will help lead towards finding a cure for a wide range of brain tumours.
Our team at the University of Plymouth Low-Grade Brain Tumour Research Centre are researching a number of molecular pathways that influence immune system function, tumour metabolism and tumour growth in a range of low-grade brain tumours in children and adults.
Scientists at our Research Centre in the University of Portsmouth are looking at repurposing drugs for a number of different types of brain tumours. They are also studying mitochondria, exploring ways to ‘shut down’ these ‘batteries’ that supply energy to the brain tumours.
The team of research and clinical experts in our Research Centre at Imperial College, London, are studying the way in which the ketogenic diet works in brain cancer, which may have the potential to influence a wide range of brain tumours.
Pioneering research at our Brain Tumour Research Centre at Queen Mary University of London is focused on using GBM stem cells to help develop unique, patient-specific treatments. Their findings are expected to translate into other types of adult and paediatric brain tumours.
We also fund BRAIN UK at Southampton University, the country’s only national tissue bank registry providing crucial access to brain tumour samples for researchers from all clinical neuroscience centres in the UK, effectively covering about 90% of the UK population, and an essential component in the fight to find a cure for germ cell brain tumours.
Page last updated in October 2019.