If you can't get to the vet within an hour or so, put the sample in
the fridge. There's no need to jump to the cancer conclusion just yet. In
the meantime, don't feed a bunch of fatty foods. If you feed steak, cut off any excess fat. If your dog has a pancreas problem, fat can be deadly.
Are there any other symptoms you've noticed? Increased or decreased water intake? Constipation or diarrhea? Bowel noises? Gas? Any observations will help your vet with a diagnosis.