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This is an informative interview with Dr J. Leonard Lichtenfeld, M.D., representing the American Cancer Society, who gives a nice summary of the various treatments for glioblastoma, including a study presented at the ASCO Oncology Meeting last year about treating refractory glioblastoma (i.e. can be removed surgically) with bevacizumab (Avastin, from Genentech Oncology in San Francisco).
A glioblastoma is a very sneaky tumor that arises most anywhere in the brain but usually in the frontal half. Unlike other cancers, it does not have any boundaries that delineate the tumor from the surrounding normal brain tissue. In addition, it can grow in critical areas of the brain that cannot be removed, such as the “motor” section of the brain that is responsible for sending nerve impulses to muscles and the “sensory” section responsible for sight, speech, etc. Interestingly, tumors growing in the frontal lobe (which has to do with memory) can grow quite large, and some sections of the frontal lobe can be removed without a significant loss of mental functions
The standard treatment is surgical removal if it is localized (which is uncommon), radiation therapy, and chemotherapy. Glioblastomas are relatively insensitive to radiation therapy, although this treatment is a common standard treatment. Radiation therapy can shrink down the tumor temporarily in some circumstances. In other circumstances, a partial surgical removing (“debulking”) can remove the pressure from a growing tumor, depending on its location and size.
Because of the “blood-brain barrier”, most types of chemotherapy can’t get into the brain (which is trying to protect itself from what would otherwise be noxious chemicals). This is a major reason that these drugs can’t get across the blood vessels into the brain since it treats most drugs the same as noxious chemicals. Paradoxically, this makes the brain vulnerable to tumor growth since it is very difficult for most forms of chemotherapy to cross the blood-brain barrier and get into the tumor. A drug called temozolamide (Temodar, Schering) does cross the blood-brain barrier and is increasingly used for cancers that have not responded to standard treatment (also called refractory cancers). Having bevacizumab (Avastin) as a second drug gives these patients the opportunity for a “second-chance” response that might prolong their life or protect them a little longer from debilitating symptoms of the tumor as it grows.
One can understand from this description that these tumors are extremely stubborn and difficult to treat. Even those that can be removed surgically have a high rate of recurrence. Radiation to the brain can cause permanent damage, especially after a few years. Only a few types of chemotherapy will get into the brain in sufficient concentration to cause any response. This is a tumor that requires highly specialized care, usually in major centers that specialize in brain tumors.
Progress is being made and there is hope.
For more information about Avastin, see the related blog titled:
“An Important Advance: Avastin (Bevacizumab) for Brain Cancer Treatment.”