Studies have indicated the following 2 important things.
Obesity (especially post-menopausal weight gain), late menopause, and hormone replacement therapy or HRT (exceeding 5 years) increase breast cancer risk.
On the other hand, a diet rich in soy isoflavones (eg. genistein, which is knowwn to have anti-breast cancer effects), reduces breast cancer risk.
Moreover, a nutrient-dense diet made of fruits, vegetables, legumes, grains and nuts also reduces the risk of all cancer.
(Source: Dr Amir Farid Ishak, My sister’s cancer, The Sunday Star, 12 June 2011)