Mimi, changes in your breasts at age 16 are very, very commoon. Lumps, bumps, sore spots... your hormones are working overtime, your breast tissue is growing and maturing, and the results can be pretty crazy at times! At your age, breast cancer is increibly rare - while hormonal changes are common. Kudos to you for being aware of a lump in your breast, as that's the way we safeguard ourselves as we get older. That said, I would doubt very much it's anything to worry about. But, rather than stress and be scared, why not see if your mom (or you?) can make a doctor's appointment? The doctor can explain to you what's happening - what to look out for, what to accept as normal change, and how to tell the difference. Good luck - PJH