Glioma is a common type of brain tumor that originates in the glial cells of the brain. These cells form the tissue that surrounds and supports neurons in the brain. Glioma accounts for around 33% of primary brain tumors. This form of brain tumor can affect an individual at any age, although it is more common among adults and slightly more common among men than women.
The treatment approach to glioma depends on the size, location and grade of the tumor. Sometimes, the glioma is very slow growing (low grade) and may not require treatment unless it starts to grow more quickly or cause symptoms. High-grade gliomas are fast growing and aggressive tumors that may require treatment with a combination of surgery, radiotherapy and chemotherapy. Those with high-grade tumors generally have a poor outcome due to the high rates of recurrence.
The techniques typically used to diagnose glioma include assessment of medical history and symptoms; a neurological exam to test balance, reflexes, vision, hearing and cognitive ability; brain scans using magnetic resonance imaging and computed tomography to create detailed images of the brain; and a biopsy to test small samples of the tumor under a microscope.
Aside from the grade of the brain tumor, the treatment a person receives will depend on the following factors:
- How much of the tumor can be surgically removed
- The position of the tumor
- The effects of the tumor on overall health and wellbeing
Treatment for glioma involves a team of individuals from multiple disciplines including neurosurgeons, radiotherapists, neuro-oncologists and pathologists.
As low-grade gliomas can sometimes grow very slowly, treatment may not be required immediately after diagnosis, unless the tumor is causing symptoms. Initially, a patient is therefore monitored using MRI scans to assess how quickly the glioma is growing. This is referred to as “watchful waiting.” In cases of very slow-growing tumors, treatment may not be necessary until months or years later and in some older individuals, the tumor may grow so slowly that treatment is never required.
If the tumor does start to grow more quickly, surgery may be of significant benefit to patients. Overall, about 50% of patients with low-grade glioma can expect to need surgical intervention within two or three years of their diagnosis. The surgeon removes as much of the tumor as is safely possible in a process referred to as “debulking.” If it was possible to completely or almost completely remove the tumor, then no further treatment may be required, although the patient will still need regular monitoring using MRI scans. In some cases, adjuvant radiotherapy may be required and this is more likely when the following factors apply:
- Age over 40
- Large amount of tumor remaining after surgery
- The presence of symptoms such as weakness in a region of the body
The outlook after surgery for glioma that were slow growing is generally positive, even in cases where some of the tumor still remains. Slow growing gliomas can take many years to start causing symptoms again and almost 50% of patients with low-grade gliomas that were only partially removed still live for at least 10 years after they have undergone surgery and radiotherapy.
For the very fast growing, high-grade gliomas, treatment involves surgery to remove as much of the tumor as possible, which is followed by radiotherapy and in some cases chemotherapy.
Although radiotherapy cannot cure glioma, it can be used to control the tumor for as long as possible. The radiotherapy is carried out for five consecutive days each week, over the period of a few weeks. For individuals with an generally poor health status, the radiotherapy course may be shortened and only last for two weeks. The radiotherapy slows tumor growth and therefore delays disease progression and the development of symptoms.
In cases of high-grade glioma where at least 90% of the tumor can be surgically removed, a small chemotherapy implant referred to as carmustine may be put in place during the operation. Although this implant can improve survival, the therapy is associated with uncomfortable adverse effects.
For those with a generally good health status, chemotherapy capsules called temozolomide may be used after surgery for several months and in combination with radiotherapy. Alternatively, a physician may decide to keep temozolomide in reserve, as a treatment option they can apply if the tumor starts to grow more quickly. Chemotherapy is successful in shrinking or controlling tumors in around one third of people after they have undergone surgery.
Examples of therapies currently being developed include gene modification and oncolytic virus therapies. For the latter, retroviruses and adenoviruses are used to carry targeted drugs directly to cancer cells which are then destroyed, while sparing any healthy surrounding cells.