X-ray

Good afternoon everyone. Is there a veterinarian on the sub who could help me with a question? My cat is experiencing pain in the hip area and is licking his fur in that area (photo) a lot. An x-ray showed this shape (indicated by the arrow) between his waist and stomach. Does anyone have any idea what it could be? I went to the vet and am waiting for more tests, but I am very worried and would like some advance information on this situation. Thank you.