Worries/Questions regarding Mastectomy

Thank you all for your comments. I feel I’m thinking if the cancer is gone from my breast why do I need a mastectomy especially as I am and will be taking anti cancer medication Herceptin for 12 months & Tamoxifen for 5-10 years. And if there is still microscopic bits of cancer in my lymph nodes won’t they be killed by the anti cancer medication & if they aren’t killed by it why am I taking it and risking the possible health problems associated with these two medications. The Oncologist said that I would need to take the herceptin & Tamoxifen even after a double mastectomy just to be sure. The Surgeon also wants me to have radiation after the surgery just to be sure, it just seems so excessive to me. And none of it guarantees that I will be or stay cancer free. I’m just feeling completely overwhelmed by it all & the decisions I have to make. I haven’t seen the surgeon since the MRI but he previously would not consider a lumpectomy due to the original size of the tumour.