American Cancer Society
American Cancer Society: Overview: Breast Cancer
This excellent site covers all the issues related to breast cancer. Topics include the causes of breast cancer, risk factors, prevention, early detection, diagnosis, staging, treatment, questions for your doctor, after treatment, and so on.
Aetna Intelihealth
Aetna: Inteli Health: High Risk of Breast Cancer
Explains a couple of the treatment options for women who have an unusually high risk of getting breast cancer.
Macmillan Cancer Support
Cancerbackup: Breast Cancer Information Center
This impressive site offers a clear and concise explanation of the causes, diagnosis, and treatment of breast cancer.