The brain is very well protected form potentially damaging organisms or substances circulating with the blood stream and even from an attack from the bodies immune system. The protective mechanisms that under normal circumstances prevent damage from the nervous system, represent a major obstacle if there is a disease such as a tumor within the brain. Several strategies have been developed to circumvent this barrier.
Intrathecal Administration of Chemotherapy
Injection of chemotherapy into the 'subarachnoid' space ['intrathecal chemotherapy'] is necessary when systemic cancer (such as lung or breast cancer) or, less commonly, cancer of the brain spreads to the fluid surrounding the brain, the cerebrospinal fluid. Three drugs are available for this application: methotrexate, cytosine-arabinoside and thio-TEPA. Drugs are injected up to twice weekly. This can be done through a catheter that is introduced in one of the fluid filled spaces of the brain and attached to a permanent reservoir that is placed by a neurosurgeon underneath the scalp (Ommaya reservoir). If only few injections are necessary, chemotherapy can be injected through a lumbar puncture (placement of a needle into the spinal fluid surrounding the lower spinal cord in the lower back). Possible side effects include headache, nausea, vomiting, or seizures. Steroids by mouth (Decadron) may be prescribed prophylactically.
Chemotherapy is usually given by vein or by mouth. Alternatively, it can be injected into an artery that supplies the cancer with blood. This strategy is still being evaluated in clinical trials for its usefulness in the treatment of primary brain tumors.
Biodegradable polymers impregnated with chemotherapy
Dime-sized wafers of a polymer impregnated with the chemotherapeutic agent BCNU can be placed within the cavity that surgery leaves behind in the brain. Their use is still limited by penetration of the chemotherapy drug over only a short distance into the brain. Future developments based on this principle may prove more efficacious.
Therapeutic concentrations of certain chemotherapy drugs such as methotrexate within the brain can be achieved by giving them into a vein at high doses. Other drugs can only be given at high doses if it is followed by a bone marrow transplantation. This approach, though successful for other types of cancer, has not resulted in a better outcome in most primary brain tumors.