I have had a mastectomy in my right breast and at the time of surgery(11/07) there were lobular in situ cells found in my left breast. I have since had chemotherapy and I am now on arimidex. I have chosen to carefully monitor my right breast with mammograms and MRIs but somehow I feel at times like my left breast is a ticking time bomb and that I should be more aggressive and just have a mastectomy. My oncologist says it is my decision and that he would not advise me either way. Somehow that does not put my mind at ease. Does anyone out there have an opinion on the subject?