Gary -- I've been doing a ton of research and might be in the same boat. And I'm so torn by what seems like the cruelest choice in the world. Do I have fun with Tetters while we can, and say goodbye when his time comes? Or do I possibly give up that precious time and send him in for surgery NOW, knowing he has less than a 15% chance of coming out alive?
If, as is common with the breed, the mass is a malignant hemangiosarcoma, he has only a couple months left and surgery will probably only give him a couple months more -- time to say goodbye. But if it's a benign hemangioma, removing the entire spleen could give him years more quality life. But the malignant form is far more common. Doing nothing either will kill him.
Gary, best of luck with Sam. I hope it turns out for the best for both of us. And if not, I pray it at least goes easy for them. Pete