Considering that it's only six letters long, and half of those are cuddly-looking vowels, 'tumour' is a surprisingly big word.* When you put the word 'brain' in front of it, it becomes positively enormous.
I may be biased, but I definitely feel that modern science should devote a little time and energy to investigating the phenomenon of the Brain Tumour Face, which in my experience is virtually universal. The phenomenon is this: when you tell someone that you have a brain tumour, their eyebrows shoot up violently and their mouth goes to a perfect o-shape. They say "oh!", quickly try to get their outlying facial features under control, and then warily ask "is it cancer?" If the answer is "no" (which for me, thankfully, it is) they slowly start to relax again. They may attempt a few further questions which you are ill-equipped to answer and/or they are ill-equipped to understand. This part seems to be optional.
Possibly the Brain Tumour Face is the seventh basic facial expression, common to all peoples and cultures across the earth. It certainly is the reason that it took me so long to mention the tumour to my friends - and even then I chickened out and told most of them over Facebook (I am grateful that no-one clicked 'like'). The problem is that it then becomes a self-fulfilling prophecy; people don't use the word 'tumour' face-to-face, which only serves to increase its fear factor. Even when referred to as a pituitary tumour rather than a brain tumour, the t-word creates quite a reaction; referring to it as a pituitary adenoma merely gets you a blank look, which personally I find preferable.
Even doctors have succumbed to the power of the t-word. Unfortunately, some of the synonyms they end up employing are quite entertaining - my favourite is "lump", which always inexplicably reminds me of the slothful Onslow from Keeping Up Appearances. The first time I went to see my (very lovely) endocrinologist after an MRI found the tumour, he managed to say the t-word only once, right at the end of the appointment, although I did notice a couple of occasions where he started to say it and then quickly caught himself. Or maybe I misinterpreted him and the "tu- er- lump" really is a medical condition.
Personally, I prefer plain speaking. Admittedly, I don't call a spade a spade, but that's purely because I try to keep myself distanced from manual labour at all costs. There's a tumour in my head and frankly I am a lot more concerned about the thing itself than what it's called. It's good that doctors empathise with the fact that their patients are going through a scary time, but continually avoiding all mention of the t-word just makes the elephant in the room swell ever larger. And develop spontaneous tumours.
Naturally there are exceptions to the Brain Tumour Face rule, particularly amongst the medically inclined/drunk. One of my good friends, a medical student, tried to persuade me to go out clubbing one night with the immortal line "Your brain tumour wants you to go!"** Oddly enough, it worked.
*Of course, if you're an American it's only five letters long, so the vowel quotient is significantly reduced. Does this correspond with a similar reduction in its bigness? Answers on a postcard, please.
** Hi, Havana.