Thats what my Yellow Lab "Buck" has, He is 13 and the vet said it is in his spleen.
I took him for a walk a week and a half ago he made it about 3/4 of a mile and then fell, I carried him for about 100 yards and then set him down he went for about 100 yards and fell again I carried him another 100 yards or so to the truck. We got back to the cabin and he was fine.
I called the vet and set up a appointment, the vet weighed him and he had gone from 87# in late April to 77# last Friday. She (the vet) was worried with the weight loss, she did some blood tests and that was her diagnosis.
This means that he has at the most 3 months, I am going to miss him big time he has been my most consistent hunting partner getting his first grouse when he was 7 months old and lives to hunt.
Buck will be getting a few extra treats in the next months.
and maybe a few extra table scraps.