sr7628, I just wanted to add that there is not a lot out there about the efficacy of treating mast cell intestinal tumors in kitties because it is usually caught too late to do anything--I got this straight from the vet. The mast cell tumor spins out histamines and other chemicals that will cause ulcers to form in the intestines. Those ulcers will eat through the intestines and cause the bowels to leak--this is when most cats get diagnosed. It is really too late to do anything at that point. That is why this disease is reported to have such a poor prognosis. Please do not be discouraged by the poor survival/prognosis rate. It sounds like Klaus's disease, like Kitty's, was caught very soon.
Also keep in mind that the lack of information about how to treat mast cell could also be the reason that there is little out there to suggest that chemo is an effective treatment. The first surgeon I spoke to told me there was little point in operating to remove the tumor because the prognosis would still be 2-5 months. Out of desperation I went to see Dr. Rau about treating it with chemo. Dr. Rau told me about an unpublished paper that one of her colleagues from vet school had written which found that surgery is beneficial treatment for mast cell tumors. Dr. Rau said if it were her cat she would do surgery and chemo. I listened to Dr. Rau and here I am 4 months later with a healthy Kitty.
I hope you will get a second opinion on the chemo especially since Klaus still has that lymphnode with mast cell that couldn't be removed.
I can't remember if I mentioned it in an earlier post or not, but Kitty also takes a steroid everyday. I think it is called prednisolone.