Scientists from the Centre for Research on Women's Health in Toronto led the study which looked at women with the BRCA1 and BRCA2 gene mutation.

BBC: Tamoxifen 'cuts genetic cancer risk'

But for the average breast cancer patient who has neither the BRCA1 or BRCA2 gene mutation nor a close relative with breast cancer (Jolie's mother, for example, died from ovarian cancer), the risk of a new breast cancer in the nonaffected breast is less than 1%.

CNN: When removing breast is not the answer