There was a lesson horse at my barn that had very very bad melanomas. They were on the side of his face/upper neck area, and were very large and noticable, larger than pingpong balls and clustered together. They never bothered him until recently. He collapsed during a lesson because one of his melanomas was pressing on an arterie in his neck that fed his brain, and he was immediately retired.
The picture doesn't look like Rocky's melanomas, his were mostly under the skin and rock hard. His were also much larger than shown.
There is something about the outside of a horse that is good for the inside of a man. ~Winston Churchill