Fibroadenomas are the predominant cause of these lumps. They are caused by hormonal changes and they are not cancer. They can be discovered on their own due to fluctuating hormones when a woman's period cycles. They are painless, moveable, and without any problem. To be perfectly sure, one should go to the hospital and get it examined thoroughly. Even if it is frequent the hospital may demand additional tests. Keep in mind not to freak out but you'll require a professional check for any changes in your breasts that are unaccountable by logic.