42 year old, diagnosed 2cm fibroadenoma today (uss and initial biopsy results-full awaited) after finding lump 1month ago had negative screening mammogram 3 months ago, should this not have shown up then? how quick do they grow?

A "2 cm fibroadenoma" which is not accompanied by a cluster of calcium deposits may blend in with fibrocystic breast changes (FCD), especially in a woman at "42", who is not on oral bcp's, which accentuates the amount of FDC in breast tissue, b/c of the increase in estrogen production stimulating breast tissue b/c of aging eggs in the ovaries requiring more stimulation to cause ovulation.