It is a hard decision, and none of the rest of us are vets. I must admit that some things don't make sense to me, for example if it was a tumour that burst why is it still palpable? If it is likely to be fatal, why is he eating and looking fine now? And, rats being so small, is it possible to know that a tumour is on the spleen? If it weren't for the risk of it being a fast-growing tumour, you would want to wait til next Monday for a second opinion.
It seems to make sense to others on the Forum with a lot more experience than I have, so you don't need to take my doubts seriously. But those are the questions that I would be asking if it were my rat.
