My boyfriend has about five to six of these hard circular (but flat) growths under his skin on his shoulder, back and neck area. When you press on one it feels like a hard disc under the skin. Is this a cyst of some sort? anything to worry about. Cancerous?

Sounds like just what you think! Cysts! He needs to at least have them excised so they dont get imflamed or get larger. Cysts have a sac they form in also and you want to have it removed along with it!