Possible fibroadenoma on ultrasound (42 year old)

I am 42 years old.  I recently had a routine mammogram which showed some asymmetry in the right breast.  I then was sent for a spot compression mammogram and ultrasound.  The place in my breast that was at issue in the first mammogram disappeared on the compression mammogram, which was a relief.  However, the ultrasound showed what may be a fibroadenoma in the right breast (1 cm in size) that was not detected on either mammogram.  My first question is, is this unusual for an ultrasound to show a fibroadenoma that a mammogram did not?

I saw the ultrasound image of the possilbe fibroadenoma.  It is perfectly oval and symmetrical with regular edges.  My second question, is does that sound like what a fibroadenoma would look like on ultrasound?   The radiologist recommended an ultrasound guided biopsy, but my ob-gyn instead referred me to a breast surgeon to review the films and provide a recommendation of whether to do the biopsy, or wait or some other course of action.

Any thoughts on whether to worry and what a good course of action is?

Thank you.

[Cleveland Clinic]

Dear sensible1:  A fibroadenoma is a benign (non-cancerous) growth. Fibrooadenomas are distinct on a mammogram or ultrasound and when aspirated - no fluid comes out. As long as the doctor is sure it is a fibroadenoma, there is no need to remove the lump. In 50% of the cases fibroadenomas will go away on their own within 5 years. In others, the life of a fibroadenoma is about 15 years. In teenagers - the tendency is not to remove fibroadenomas. In middle age women, the tendency is to remove the fibroadenomas to be sure they are, in fact, fibroadenomas.  So depending on the individual situation, putting the findings in context, a suspected fibroadenoma might be biopsied to be sure of what it is. An ultrasound cannot always make a diagnosis of fibroadenoma with certainty.