Don't worry too much, mate. I just had ultrasounds detect all manner of lumps (possible fibroadenomas, cysts, etc.) in both of mine - my GP was a bit concerned as the radiologist recommended an FNA biopsy - but since I'm having them removed (breasts) in top surgery in January, there's really no point.
Sometimes there's not much you can do. Having them removed may or may not mean that they return - but cysts are common and quite different from cancer. From what I've read, having fibrocystic breasts doesn't necessarily increase your risk of developing cancer, so I wouldn't worry about it unless you had a reason to. Good luck.