Hi Rachel,
Firstly, I am also new to this forum. I just stumbled on it today and saw your post. 18 months ago I was diagnosed with Fibrous Sarcoma of my left maxillary sinus. Yes, it is very rare indeed, very difficult to deal with and is not caused by lifestyle. I had all the tests that you mentioned and this was followed by I had an operation. Unfortunately, last year my tumour came back - which is again unbelievably rare - but I have managed to get through both well. I am getting stronger now and looking forward to getting back to normal (as much as possible). I'm also from Australia, so if you have any questions, don't hesitate to ask - I'd like to be of help. All the best to you.
Margie