Cancer of the breast is the most common sex-specific neoplastic entity in the United States. It is estimated that about 50,000 new cases are diagnosed annually, and approximately 25,000 deaths are attributed to breast cancer among the 91 million females of the US population. The lifetime risk of breast cancer for a woman is 5.5 percent. This means that in one of every 18 women breast cancer will develop during her anticipated 72 yr of life. Statistical Data One of the striking characteristics of breast cancer in the United States has been the very uniformmortalityrate recorded during the past 30 or more years.1,2In terms of absolute numbers and gross mortality rates, there has been a steady increase. Thus, in 1930, there were 11,000 deaths and a crude annual death rate of 18 per 100,000 females, whereas, by 1958, there were 22,500 deaths and a