I was fine when he said it was cancer. I was still fine when we discussed different types of cancer and the prognosis for each. I was even fine when we discussed the relative merits of compassionate euthanasia. What got me was this line in the printed client instructions:
Indulge him in whatever he wants. Do not hesitate to take him to the park in the sunshine.
Having been in the same exact shoes very recently, you have my empathy and big hugs to the entire family (4 legged especially).