Hi Julia, sorry to hear you are going through all of this. I did not have a malignant tumour however my borderline tumour had either spread or I was growing a second one close to the original one. I had an mri but it was only a breast mri which showed no other tumours. I chose to have a mastectomy because no one could give me any guarantees that there weren't any other tumors in there or that I would grow more. You have some difficult decisions to make but you need to make choices that you feel are right for you! There are two support groups on facebook that have lots of members and lots of information about all the different treatment options. Just search phyllodes and they should come up. I also have some written info that I can email to you if you want some more info. All the best. Cheers Katie.