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This is Your Brain on DrugsDrug Therapy -- Background Information
However, it is important to understand why there has been so much interest in drug therapy. Most neurosurgeons agree that the most common brain tumors in adults, malignant gliomas, are difficult if not impossible to resect because of their tendency to spread microscopically away from the main tumor mass. Radiation therapy, though it clearly improves survival, does not cure malignant glioma despite modern techniques and the use of drugs called radiosensitizers to increase its effectiveness. Drug therapy, including chemotherapy, immunotherapy, biological therapy, anti-angiogenesis therapy, has improved survival of some, but not all patients; and it has been difficult to determine before treatment which patients may benefit. There are some types of brain tumors which respond well to chemotherapy: they may dramatically regress or even be cured. Primary central nervous system lymphoma is one example of such a tumor, but it is unusual in that respect. Although further research in the molecular biology of brain tumors may shed some light on which patients may respond to certain drugs, at this time it is still a "give-the-drug-and-see-what-happens" approach.
The curability of any tumor with drug therapy depends on a set of factors including:
The amount of tumor present after surgery or after radiation therapy is potentially very low. Treating with drug therapy at this time may provide the highest benefit, before any residual cells have had a chance to grow back. Many studies have included chemotherapy immediately after other treatment but it is difficult to tell if the drug is effective until several weeks or months have passed because there may be no tumor visible on MRI at the beginning of chemotherapy. Only a randomized group of patients taking the drug, compared with another group not taking the drug, would clearly determine its effectiveness. The amount of the drug given and the time interval over which it is given is referred to as "dose intensity." A high dose given infrequently may be ineffective at controlling the tumor because the tumor cells that survived the treatment will rapidly regrow. Some drugs are "schedule dependent", meaning that their effectiveness at controlling the tumor may require spacing the drug out over days or even weeks. Not all chemotherapy drugs are effective against all tumors. Many of the common drugs used in the treatment of breast cancer, for example, are not used in the treatment of brain tumors. Even within a brain tumor, the cells are different from each other and that is why two or more drugs are often used in combination or in sequence to treat brain tumors. Finally, the lucky patients who have a disappearance of their tumor while taking chemotherapy may be unpleasantly surprised that their tumor has regrown, even as they have continued their treatment. Some tumors, particularly some glioblastomas, appear to be resistant or "immune" to the effects of chemotherapy from the beginning of treatment. That is why it is so important to continue close monitoring of brain tumors while on chemotherapy treatment, sometimes as often as every month. Is it possible to cure malignant glioma with chemotherapy? Yes, but it is extremely difficult because of the side effects of chemotherapy. For example, very high dose chemotherapy with bone marrow transplant has been used in the treatment of malignant glioma. Intra-arterial chemotherapy has also resulted in some long-term survivors. However, both of these treatments may cause major organ damage which can be permanently debilitating or fatal. |
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