Types Definition of breast cancer: Cancer that forms in tissues of the breast, usually the ducts (tubes that carry milk to the nipple) and lobules (glands that make milk). It occurs in both men and women, although male breast cancer is rare. 
Estimated new cases and deaths from breast cancer in the United States in 2008:
- New cases: 182,460 (female); 1,990 (male)
- Deaths: 40,480 (female); 450 (male)