old dog groaning noises.

My dog, Elmo, is 12 years old, a German Shepherd, Husky mix. He is about
the size of a large German Shepherd but about 10 pounds overweight, I am
trying to limit his calories but he gets such pleasure from food. As far as
exercise, everday we take a morning and evening walk of 1 kilometre. He does
not really enjoy the walks that much but does them for me. He pants a lot
and slows down and stalls and sniffs but when we turn around to head back
home, he suddenly has more energy and he speeds up and almost prances.

About a year ago, I noticed a lump in his thorax, just below his rib cage on
the right about an inch from the centre line. At the time, the doctor said
he thought it was a fatty lump and not to worry. I think it has gotten
larger. I do not want to put my dog through the stress of surgery at his
age.

Recently he has begun making very small groaning noises at night. Since he
sleeps on my bed, I notice this change. He will make a small groan and then
switch positions. After much groaning and switching, he finally goes to
sleep. But then he wakes me up in the middle of the night with the switching
of positions. I have given him a coated aspirin at bedtime. It did not help.

What do I do? Surgery is very invasive and it might take his life. Elmo's
last surgery to remove a similar lump which turned out to be a fatty, non
malignant tumour, was about 3 years ago. The surgery really depressed him
and he took a while to come back to full strength. But if this is cancer or
a rapidly growing tumor, this will also take his life. If it is a fatty
tumor and it is pushing on his lungs or heart or other organs, that could
account for his not liking long walks or his shifting positions at night and
the groans. Or maybe this is all part of the aging process in a dog. How can
I tell if he is in pain or just giving old age groans. He eats fine and
seems happy. Please let me know your opinions. Money, thank goodness, is
not a factor. I want this dog to be as happy, always, as he has made me.
Thank you.