Fibroadenomas - do they need to be biopsied or better to be removed if the woman is above 40?

I have been planning to get a breast fat transfer and my surgeon requeated a breast ultrasound although I had a mammogram few weeks ago &was clear.the ultrasound showed a few cysts in the left breast and a 2 cm fibroadenoma in the right one.she insisted it looked benign but still suggested a biopsy making me worry and am trying to keep positive .How can this be missed by a mammogram ? I booked with a breast surgeon do u think it is better to just remove it altogether to stay on the safe side .