Hi. My 13-year old son found a small lump directly under his left nipple maybe a 8 months to a year ago. He is pretty skinny. He says it doesn't hurt and he isn't experiencing any other symptoms; it's maybe 1.5 cm in diameter and hasn't really changed in size (He says that one wouldn't be able to see it at all). It also seems to be attached to the skin. We consulted his pediatrician about this, but it they said it was just breast tissue formed during puberty. Could this be wrong and should we be worried?