Fish.....cancer? What could this be?

wow, that looks like someone pecked him, but I do have a Dojo that had an open wound form like that. It eventually healed and he has lumps on him now. I had him in the qt for a month or two. He is still skiny, but is doing much better after reuniting him in the tank w/his buddy. Most ich treatments contain cancer causing ingredients, it doesnt surprise me that fish would get cancer.
 
I had the same thing happen. several months ago, my largest black skirt started growing a lump on her side, and also a little growth on her face/chin. both areas were black in color, and both continued to grow. finally, the lump started to rupture (an abscess or tumor) and her mouth fell off on the same day. literally her jaw was just dangling for a little bit and then broke off, and her face was just open. i put her down that day. aside from the obvious physical damage, she never acted or appeared sickly. always swimming, chasing other tetras, very perky. kept eating right until her last day.
 
AquariaCentral.com