An unusual bump above my dog's left shoulder

[Yoshi4002]

Me and my family have noticed the bump on Shadow, who is a Black Lab, a few months ago. I remember Dad telling us that the vets told him it was cancer. however, I've questioned that initial diagnosis for the past month or two, since Shadow's eating habits (two meals a day, drinking water) has not changed. His behavior has not changed either, as he remains as energetic, and tendency to become overexcited, as he's always been. The bump does increase in size on some days, but shrinks back down on other days. Though I am relieved that he's fine, I'm still so curious about that bump. What is it? I'll also try to provide a picture of it, at a later time.

[Margot49]

What reason did your Dad have for saying it was Cancer? Was Shadow taken to the Vet? Was an aspiration biopsy or x-rays done?  It sould be any number of things. If Shadow hasn't been to the Vet, someone should take him and have this checked.

[Yoshi4002]

I should've worded that better. Dad TOOK Shadow to the vet, and the vets told him Shadow had cancer. I'd give more details, but I have a poor memory and I know I wasn't there, but dad did take him there.