Breast cancer is the most commonly occurring cancer in women and, until recently surpassed by lung cancer, was the leading cause of cancer-related death in women. It is the leading cause of death in women aged 39 to 44 years. The American Cancer Society has estimated that there will be 135,000 new cases of breast cancer and 42,300 breast cancer-related deaths in 1988. It is now predicted that breast cancer will develop in one out of every ten women in the United States. Given the clinical and public health significance of breast cancer, annual screening with mammography and clinical breast examination is recommended for women aged 50 and older to reduce breast cancer mortality.