The decline in breast cancer incidence: real or imaginary?

Breast cancer is a major global problem, with nearly 1 million cases occurring each year. Over the past several decades, the disease's incidence has risen worldwide, increasing in developing and developed countries. This rise in breast cancer incidence has been attributed to changes in lifestyle and reproductive factors and to the dissemination of population-wide mammographic screening, which facilitates diagnosis. Recently, a decline in breast cancer incidence was reported in the United States and several other developed countries, and a substantial reduction in menopausal hormone therapy use was proposed as a possible cause. However, significant controversy remains as to the timing, causes, generalizability, and longevity of this reported decline in incidence.