Hi B, I understand where you are coming from, and have been there too. I had stage 2 grade 3 breast cancer diagnosed nearly five years ago. I first had a lumpectomy, but because it was bigger and more aggressive than originally thought, I went back and had a full mastectomy and level 1 lymph node removal (10 nodes). All nodes were clear, including the first sentinel node. I had 4 rounds of chemo and then 9 months after original diagnosis, went back and had a second mastectomy and insertion of tissue expanders. I was very worried about getting a new primary in the remaining breast, and as the mammogram had failed to pick up my breast cancer, I found it hard to relax. Just prior to my prophylactic mastectomy, I had a mammogram, followed by an ultrasound. The mammogram was clear, but the ultrasound picked up a suspicious lump. This was exactly what happened the first time around. Again I went through core biopsy, and regret that I had waited. Fortunately this time it wasn't cancer, but if ever there was a sign that I needed, this was it. I have never regretted my decision, and every time I hear of someone finding a second breast cancer, I am grateful that I do not have 2 breasts. Everyone is different, but for me, this second mastectomy has given me and my husband peace of mind. I agree with Robyn, that this won't prevent a recurrence, but it will prevent a new primary, so I felt that this was something I could control.
I am happy with my reconstructed boobs, and I am about a C cup, so look just the same in clothes as I did before my mastectomies. I wish you luck with your decision making.