This Is A Question For An Oncologist. Five Years Ago

This is a question for an oncologist. Five years ago I had estrogen-sensitive breast cancer, treated by lumpectomy, radiation, and tamoxifen. At the end of January I'll finish my five years of tamoxifen. I'm lactose-intolerant and for maybe 15 years have been using soymilk with my breakfast cereal. Now I'm considering a diet plan that is based on Medi-Fast and is highly dependent on soy products (plus one meal of lean meat and vegetables a day). When I stop tamoxifen, should I avoid excessive soy, or would this diet plan be safe for me as far as the likelihood of recurrent breast cancer is concerned? Is the phytoestrogen (isoflavones) in soy a danger or a help in avoiding my kind of breast cancer? I'm reading indications both ways.