The worry is understandable. Have you talked with your oncologist about the risks in specific terms? My mastectomy was over 5 years ago. I discussed the option of removing the other breast some time later - in my case (and cancer is very variable, so what applies to one may not apply to another) my oncologist advised that IF I were to get another cancer (as distinct from a recurrence) it was as likely to be elsewhere in my body as in my other breast. I spent a year with a persistent seroma and related infections so I am not mad keen to have more surgery without a pretty clear benefit. I think many of us can understand the "6 month extension period". It does diminish over time in my experience. But you are in the best position to know your own feelings, and I am sure others here will share their experiences, to help you weigh up the pros and cons. Best wishes for whatever decision you make, these are not easy.