I took my dog to the vet for a large lump, and she did a biopsy and said it's a lympoma - a fatty tumor. Then she felt around and said here's another one, and another one,....
It's getting bigger, but she said not to worry about it. I had one of them on my leg that I had removed because it was digging in to the muscle, but otherwise they don't hurt. This big one doesn't seem to hurt the dog, either.