Breast Cancer treatments

How does a pathologist decipher a fibroadenoma from a cancer? My lump was described as a probable cyst by the radiologist. My hospital billed us for the removal of a fribroadenoma.  So I am assuming when under a microscope something in the cell stucture suggested it was cancer. It was 2cm. removed with clear margins no     lymph node involvement ER+.  I have undergone radiation and will start Arimidex.  New cancer guidelines seem to suggest hormone therapy alone might be possible for these types of cancer.  What do you think?

[CCF-RN,MSN-rf]

Dear jerryM:  A fibroadenoma is a benign tumor - not cancer.  If the hospital billed you for removal of a fibroadenoma - this must have been a preoperative diagnosis.  In other words, at removal, there must not have been any obvious evidence of malignancy.  Cancer cells are usually distinct from benign cells under the microscope.  As you do not mention the final pathology report(which must mention the type of malignancy), we cannot comment on what the treatment recommendations should include.