Hi April - At your age, breast cancer is almost unheard of. It's good to be aware of changes in your breasts, especially as you get older; but right now, the thickness you feel is probably muscle, scar tissue, perhaps fibrous tissue, or something else. As for what questions you should ask - tell the doctor you want to know what the thickening is, and if it's something you shuld be concerned about. Hopefully you'll get some answers. Good luck - PJH