Growth on 15 Year Old Cat

Our oldest cat is 15 1/2, and we noticed a growth on the outside of her mouth yesterday. We have noticed no changes in her: no lethargy, eating, drinking, and using the litter box just fine. Anyone know what this might be?

No idea but you should email the picture to the vet for an opinion. The vet may want to see your cat to check the growth more closely.

It could be a harmless benign tumor, which is VERY common in cats her age, or it could be the beginnings of cancer. To be sure and to catch it at an early stage, I would see a vet, they have seen so much they can usually tell you which it is with an exam. I know how hard it is to bring in and stress a cat her age, I have a 15 1/2 year old too, maybe you could time it and have a health exam and any tests that may be needed at her age at the same time. It is fortunate it is on the outside of her mouth and not on the hard palate. If it is soft and movable the chances it  is cancer are small, those tumors are usually hard and immobile. We had a stray that showed up with very advanced mouth cancer and he lived a year and a half relatively happily on prednisone which kept the cancer from getting any bigger, so there is hope, especially if it is caught early and can be removed.  I'll pray that it is benign,  give her a kiss from me, all the luck and keep us posted!