My grandma beat Lymphoma twice, the second time when she was 70. Not breast cancer, but it's just a testament that cancer can be beaten.
I agree with a post above, I think the five year thing just means five years free of cancer and the patient was considered 'cured', so they closed the file.
Also, I've always wondered, wouldn't it just be easier to remove your breast right away, rather than waste time with a biopsy and a chance of it spreading in the mean time? I would think peace of mind would be well worth a falsie. Pretty sure you can keep your own nipple, unless the cancer is right in that area or something.