Dear RGLRGL: If a lump can be felt, it usually needs further evaluation. Whether or not it is biopsied will depend on how it feels to the breast surgeon and the level of concern both-the surgeon's and yours. This could be cancer but, at your age, it is more likely to be a number of other things.
mammograms are, basically, to find things you can't feel. Ultrasounds, basically, are to tell if something is liquid or solid, and are best used on something that shows on mammogram but can't be felt, because if it can be felt, a little needle (see below) gives more useful info. When there's a lump, it doesn't matter what those tests show (except if the ultrasound shows it's liquid, in which case it's a harmless cyst): one still needs to make a decision based on the lump itself. Whether the surgeon would biopsy or not would depend largely on how it actually feels, and on your own level of concern. A simple thing is a fine-needle aspiration: if it's a cyst, fluid comes out and the lump is gone. If it's not a cyst, then a sample of cells can be removed and looked at under the microscope. If the lump feels benign, the cells are benign, and the mammogram is benign (which it already is) then the chance of missing cancer is nearly zero.