Primary tumors of the CNS (central nervous system) account for approximately 2% of human cancers. The most common type of CNS tumors in adults are malignant gliomas, which are divided into low grade (grade 1 and grade 2 glioma) and high grade (grade 3 and 4).
Classification, Grading and Staging of Gliomas
Classification of brain tumors depends on the cell type a tumor arises from:
- astrocytic tumors
- mixed glioma
Grading of brain tumors relates to their growth rate. The greater the degree of cellular abnormality, the higher the grade and the faster the tumor is likely to grow. Low grade gliomas (grade 1 and grade 2 glioma) are the slowest growing. Low grade tumors are regarded as benign and high grade as malignant. Malignant gliomas generally have a higher risk of recurrence and are more likely to spread to other areas of the CNS.
Staging of a cancer is a measure of how far the malignancy has spread from its origin. However, at present there is no standard staging system for brain tumors. The TNM (tumor-node-metastasis) system used in other cancers is not appropriate for gliomas since they rarely spread into the lymphatics. A staging system has been recently proposed, using histological grade together with unfavorable features such as patient age, tumor location, proliferation and molecular markers. For example, a histological grade 2 together with no unfavorable characteristics, would be classified as a stage 2 glioma (or group II).
Symptoms, Diagnosis and Treatment
Symptoms will depend where the glioma is located, but a patient may experience the following:
- nausea and vomiting
- lethargy and irritability
- gradual decline in cognitive ability and motor skills
- changes in personality and behavior
Diagnosis is by standard histopathology (microscopic examination of the tumor tissue). Detection of molecular markers can help determine prognosis. CT and MRI scan are also used, with MRI being particularly effective at viewing the detail of the CNS. MRI can also be used to track the effectiveness of treatment.
Treatment: although less aggressive than high grade brain tumors, low grade gliomas (e.g. grade 2 glioma) may still require surgery, radiotherapy and chemotherapy.
Risk Factors for Glioma
- Age: as with most cancers, risk increases with age, although gliomas do occur in children.
- Genetics: approximately 5% of brain tumors can be attributed to genetic factors. Close relatives of patients with CNS tumors have a greater chance of developing gliomas.
- Immunology: people with a weakened immune system have a greater risk of glioma.
- Environment: the only proven environmental cause of brain tumors to date is radiation exposure. Other possible risk factors have been researched, but results are inconclusive.
Molecular pathology in adult gliomas: diagnostic, prognostic and predictive markers, by M.Jansen, S.Yip & D.Louis. The Lancet Neurology, 2010, Vol 9, P717-726
Cancer Research UK website www.cancerhelp/org/uk
The Royal Marsden NHS Hospital Trust website www.royalmarsden.nhs.uk/cancer-information/
A pragmatic clinicopathobiological grouping/staging system for gliomas: proposal of the Indian TNM subcommittee on brain tumors, by T.Gupta, R. Sarin, R.Jalali , S.Sharma, P.Kurkure, A.Goel. Neurology India. 2009, Vol 57, P247-51.