I had a friend who had a breast fibroadenoma when she was younger. Of course, when she first found the lump she was totally freaking out, and her doctor was a little worried too, because it seemed to be growing.
However, she did the whole aspiration/breast biopsy thing and it turned out just to be fibroadenoma, thank God!
Apparently what had happened was that she had accidentally caused some kind of trauma to the breast several months before, without noticing it -- the doctor said she could have even just hit it during her sleep -- and that caused somethign to go wonky with the cells, causing the breast tumor.
We were just glad that it wasn't a carcinoma of the breast or anything -- and of course, now we're all up on our breast pathology, which we obsessively studied while waiting for her results, which I suppose is also a benefit.