A brain tumour is the result of abnormal growth of cells in the brain, unfortunately, we’re not certain why it happens but sometimes it can happen because of a previous cancer. The reason it is really bad is because it starts taking up space in the brain and squashing the surrounding bits of brain to the side, this can stop those bits of the brain working like they normally do or can break brain connections. This then causes the patient to have different behaviours.
Also, tumours from other parts of the body can spread to the brain as well. Brain cancers I think have one of the worst survival rates- this is mainly because surgery of the brain is very delicate, hard to do, and sometimes can not be performed. The other option is to use drugs- hwoever this is a problem because the blood brain barrier makes delivery sometimes difficult. Its a cancer that needs more funding and researcgh (in fact, it might even be worth while for me to do some brain cancer research as I have had a couple of uncles that have died from it- meaning I might have some genetic presdisposition).
ON good news, one durg for melanoma (the same one that is on my profile) has been shown to be able to cross the blood brain barrier and has shown positive responses. However, this drug is only effectove for patients with a BRAF V600 mutation and hence, it wont be able to be used in all situtations.