Walnuts may prevent breast cancer -- BBC

The nuts contain ingredients such as omega-3 fatty acids, antioxidants and phytosterols that may all reduce the risk of the disease.

Previous research has suggested eating walnuts at the end of a meal may help cut the damage that fatty food can do to the arteries. It is thought that the nuts are rich in compounds that reduce hardening of the arteries, and keep them flexible. Walnuts may prevent breast cancer

Walnuts May Help Keep Breast Cancer at Bay U.S. News & World Report
Walnuts May Help Prevent Breast Cancer WKBW-TV
Forbes - Science Daily (press release)