ASF's are prone to spontaneous warty tumors that erupt from the skin, and also stomach tumors. You'll see them as they age past 9 months (or so). If they scratch and make it bleed or infect the skin tumors, you will likely need to get a new breeder.

If it's not growing too quickly, and isn't prohibiting a normal life, then I wouldnt worry about it right now. My first male had a huge tumor grow very quickly in his right ear, and one in his stomach, and one on his back. He likely would have died from the stomach one eventually, but the ear was bloody, scabbed and continued to grow at an alarming rate. He was put down, and another male was left with his colony to take over.

I have science articles saved somewhere if people want to read about it, I think I found them at pubmed and..... well can't remember off the top of my head. I'd have to dig them up, but yea. Didn't read about it at the time Mike's had the outbreaks.