Precancerous Breast Cells

My mother, age 45, was experiencing pain in her left breast. After a self-examination, she discovered a large lump about the size of a nickel. She schedule a mammogram two weeks after she discovered it and the lump shrunk. It was about the size of a pea at the time she got the mammogram and it had moved. Today she went back to the doctor where she got a biopsy and was told by the doctor that the cells 'look' precancerous. She wanted to know how cells can look precancerous since she was told that they simply look abnormal meaning they could be a number of things that are not cancerous by another doctor. Though I want to know about what it could be besides precancerous because it shrunk in size, moved and she felt pain all symptoms that I didn't see associated with precancerous cells or cancerous cells.

[zouzi]

Hi,  
Your mom had a breast biopsy done which showed abnormal cells ( possibly atypical cells?)
A finding of abnormal cells does not mean that the lump is cancerous but simply that the cells in the lump are growing abnormally and could develop into cancer in the future.
Removal of the lump showing abnormal cells, is usually indicated as a preventive measure even if the risk of it becoming cancer is relatively small.Also some drugs like tamoxifen could be prescribed if her doctor advises her to take it.
Please discuss with your mom's Doctor what are her best options.
Best wishes to both of you.