It could be lots of different things! We cannot diagnose your dog over the Internet. We would only be guessing what's wrong, which will not help your dogs situation any. It could be a Tumor, Cyst, etc... Is the lump hard or soft? Can you move the lump? If there is a lump, then you need to take your dog to the vet and have it looked at. Only a vet is qualified to diagnose and treat your dog. Hope it's nothing serious! Good Luck!
