Thank you for contacting Petco Pet Education Center, formerly Petcoach with your question about Ryder. This lump could be a cyst or a benign growth. Any suspicious lumps should be examined by the vet. The vet can perform a test called a fine needle aspirate on it. To do this, the vet sticks a small needle into the lump to get a sample of its cells, and examines the cells on a slide under a microscope. It's usually painless to the animal, and relatively quick to perform. Once the cause of the lump is diagnosed, the vet can discuss treatment options if needed. Give his vet a call to make him an appointment. I hope this helps!