Is a medium slize hard lump on the back of dog normal?

It is not normal for a dog to have a medium-sized hard lump on its back. This could be a sign of a more serious medical condition. It's important to have the lump checked out by a veterinarian, especially if it is rapidly growing, has ulcerated, or is causing your dog pain or discomfort. The vet will be able to determine the cause of the lump and recommend the best course of treatment.