My 9 year old male kitty, Cyrus has had a bump on the lower part of his tail (close to his back) for a few years now that has not grown too much but I'm thinking it is just a fatty tumor as my mother's animals have gotten them in the past. When should I be concerned or what should I look for? He has had it for about 3 years, it has grown only some, he is overweight, but not obese. The bump moves mostly freely (it does not seem attached to the tail). He acts just fine, eats and drinks fine. Plays with his siblings (my other kitties), and gets plenty of love and attention all the time. My cats are indoor, so I do not take them in for shots yearly as they do not come in any contact with any other animals or the outdoors. He is neutered. Any ideas? Thank you!