Pet Health > My Rottwieler was diagnosed with agressive pancreatic ... > Animal Questions

My Rottwieler was diagnosed with agressive pancreatic cancer 2 months ago. My vet placed him on 80mg of Prednizone a day. He responded very well to the medication in that he regained his appetite and began to return to his active self. My vet told me that I could expect to enjoy him for 30-60 days after his diagnosis, and that this type of cancer was not especially painful. About 2 weeks ago(70 days after diagnosis), he began to develop blister like growths around his neck and head areas. These have gotten much worse and have spread to other areas of his body. The appearance of theese 'growths' has accelerated, so much so that they seem to appear over night. After some on-line research, I felt that these sounded alot like mast cell tumors (MCT). After speaking with my vet by phone, she seemed to think this was probably the case, but that it wasn't related to his pre-existing cancer. I just want him to be comfortable durring his final days.
My questions are: How can I determine if he is in pain or tremendous discomfort, so that I know if or when to administer pain medication?

His stomach has recently been making all sorts of gurggling sounds. Could this be related to his illness, medications, or could it just be all the 'human food' I have shared with him? (Such as ground beef and chicken breast)

This may be a hard one: Are theese two seperate conditions something that will allow him to pass on rapidly, (perhaps at home), or can I expect to have to intervine so as to avoid him suffering unnecisarily?

Optional Information:
Age: 7; Male; Breed: Rottwieler