Primary Brain Tumors
Primary brain tumors, those originating in the brain, may spread within the central nervous system (brain and spinal cord), but they rarely spread to other parts of the body. For treatment, brain tumors are classified by the type of cell the tumor resembles, the location of the tumor in the central nervous system, well-circumscribed versus diffuse nature and the grade of the tumor (WHO grading schema). Diffuse gliomas with IDH1 mutation are generally associated with a favorable prognosis.
- Pilocytic astrocytomas (WHO Grade I): They grow slowly, are well circumscribed and therefore respond well to surgical resection. Recurrences are rather infrequent in these tumors. These tumors occur more often in children and young adults as compared to older adults.
- Diffuse astrocytomas (WHO Grade II): These grow slowly but are infiltrative, which makes it difficult to resect these tumors surgically. They therefore require adjuvant therapy in many cases. They also tend to progress to a higher grade, and they occur most often in young adults (30-40 years of age).
- Anaplastic astrocytomas (WHO Grade III): Similar to diffuse astrocytomas, they are infiltrative but these grow more rapidly and spread into nearby tissues and tend to occur a decade later.
- Glioblastomas (WHO Grade IV): Glioblastomas are the most common primary brain tumors which affect the adult population and can be seen in any age group. These are difficult to treat with poor prognosis despite the standard of care (surgery, radiation therapy and chemotherapy).
Oligodendrogliomas (WHO Grade II and Grade III): They occur in young adults and have infiltrative properties but tend to do better than astrocytomas because of the associated molecular alterations (1p19q co-deletions).
Brainstem gliomas: These are tumors that form in the brain stem, the part of the brain connected to the spinal cord. They are often high-grade and are difficult to treat successfully. Brain stem gliomas that are high-grade (Grade III or IV) or spread widely throughout the brain stem are difficult to treat successfully.
Meningiomas arise in the meninges and more commonly occur in women. They are the most common primary benign brain tumors.
- WHO Grade I meningiomas are slow-growing and benign.
- WHO Grade II and III meningiomas have more aggressive clinical behavior because of their tendency to recur. WHO Grade III meningiomas are also associated with increased mortality and are more common in men.
Ependymal Tumors: These tumors can have WHO Grades I through III. WHO Grade I tumors are seen as sub-ependymoma in the brain and as myxopapillary ependymoma in the spinal cord (cauda equina); they generally grow slowly and can often be removed completely by surgery. WHO Grade II tumors are however more common and are seen in the posterior fossa frequently although they may be seen elsewhere as well. These also respond well to surgical resection given their well-circumscribed nature. Sometimes these tumors can undergo malignant transformation when they are labeled as WHO Grade III anaplastic ependymomas. Adjuvant therapy is required in these patients.
Pituitary adenoma is a very common benign intracranial tumor seen in adults. It can be functional (with endocrine symptoms and signs) or nonfunctional, or it can be micro- or macro-adenoma depending on its size. Functional ones tend to present earlier because of their endocrine symptoms and therefore are usually micro at the time of presentation. In contrast, nonfunctional ones tend to present as macro-adenomas and with visual deficits. Surgical resection is the mainstay treatment in macro-adenomas while the micro-adenomas may be considered for medical treatment.
Metastatic Brain Tumors
Metastatic brain tumors are those that originate in another organ and spread to the brain. The types of cancer that commonly spread to the brain are cancers of the lung, breast, skin (melanoma), and colon. These can present as solitary or multiple lesions. Treatment is variable from surgery alone to adjuvant radiation and/or chemotherapy.