Breast cancer is the most common malignancy among women in the United States. It accounts for 29% of all cancers in women. In 1992, the estimated new cases of breast cancer were 180,000, and the estimated deaths due to breast cancer were 46,300. There has been an increase in breast cancers at a rate of 1% per year for four decades. Since 1982, however, this figure increased to 4% per year largely due to the increasing use of mammography.
The cause for the long-term increase is uncertain. Current figures indicate that one in nine American women will develop this disease. Worldwide, the incidence of the disease is increasing between 2% to 3% per year such that by the year 2020, it is projected that between 1.1 and 1.4 million women will be newly diagnosed with breast cancer. Much of the attributable change in breast cancer incidence has been related to several interrelated factors.
These include improved efficiency in cancer registries, greater care in the detection and diagnosis of breast abnormalities, increased number of surgical biopsies being performed, and more extensive pathologic examination. In 1987, the Breast Cancer Detection Demonstration Project reported improved survival rates of 88% at five years and 79% at ten years in women who participated in mammographic screening. Findings further demonstrated the benefits of screening mammography in premenopausal women. Based on the efficacy of mammographic screening, it is expected that the incidence of breast cancer will continue to rise in the next decade.
The predominant increase in earlier detection has had an effect on the percentage of women presenting at diagnosis with smaller primary breast tumors. For example, the number of women diagnosed with breast cancers smaller than 2 centimeters in diameter with no axillary node involvement rose from 12,000 in 1982 to 32,000 in 1996. The decrease in both tumor size and nodal involvement has been identified as an important indicator of improved long-term survival after breast cancer.
The five-year survival rate for localized breast cancer is 91% for white women and 86% for black women. Overall five-year survival statistics for breast cancer in all stages are 75% and 63% for white and black women respectively. Breast cancer is the second leading cause of cancer death for women of all ages. The death rate due to breast cancer has not changed appreciably. In the period from 1990 to 2017, the age-adjusted breast cancer death remained stable at 27 per 100,000 women.
The most likely explanation for the increasing incidence of the disease coupled with a stable mortality rate is the overall improvement in breast cancer therapy. Thus, while the incidence of breast cancer is increasing, cancer treatment regimes are becoming more effective, such that women are surviving and living longer with their disease.