Even a vet couldn't tell you what that is for certain from a photo. If they suspect cancer, they'd have to look at cells under a microscope, and even then most vets send out a sample to a lab that specializes in identifying tissues and cells to be absolutely certain.
I'm afraid it's against forum rules to guess at diagnosis for things that haven't been seen by a veterinary professional. This is to help avoid the situation where someone with no veterinary training tells a poster that their dog is fine when it really needs in-person veterinary care or worse - suggests at-home treatment that could actually harm or kill the dog. There's no way to tell whether anyone posting here has any veterinary training, and it's actually illegal for vets in most countries to give medical advice to someone whose pet they haven't personally examined. Glad that he's seeing a vet soon, and I hope it's nothing serious!
I'm afraid it's against forum rules to guess at diagnosis for things that haven't been seen by a veterinary professional. This is to help avoid the situation where someone with no veterinary training tells a poster that their dog is fine when it really needs in-person veterinary care or worse - suggests at-home treatment that could actually harm or kill the dog. There's no way to tell whether anyone posting here has any veterinary training, and it's actually illegal for vets in most countries to give medical advice to someone whose pet they haven't personally examined. Glad that he's seeing a vet soon, and I hope it's nothing serious!
