Dear practo user, Avastin is definitely a drug that is used in various conditions. The drug that goes by the name Avastin(trade name) is Bevacizumab. If one wants to know the mechanism by which this drug works is that- it slows down new blood vessels formation in the problematic area ( a useful action in case of tumors). This drug can cause various side effects among which the common ones are -easy bleeding tendency in the form of nose bleeds or  bloody stools -body ache -Chest pain or discomfort etc It is recommended that if any of abnormal effect start appearing with this drug, one must consult the doctor. When asked about the use of this drug in case of brain tumors, it is prescribed in a tumor called glioblastoma which a fairly severe condition. Hope this helps. Regards.