The relationship between age and incidence of breast cancer. Population and screening program data.

Despite extensive study of breast cancer incidence, including specific studies of the relationship between age and breast cancer incidence, the picture remains confusing. This article examines not only the relationship between age and breast cancer, but also trends over time related to this relationship to discern the underlying true age-incidence pattern. The age-incidence curve changes around the menopausal period, most likely due to hormonal changes 10 to 15 years earlier, flattens out in the 40 to 50 year old age range, and then increases as age increases. Recent data showing decreased risk of breast cancer incidence at older ages, e.g., older than 75 years of age, relative to younger ages, are likely an artifact of recent increases in breast cancer screening in the United States. This picture is consistent with increases in screening and with notions of lead time created by increased screening. The increase in screening that has changed the age-incidence relationship may eventually deliver benefits to United States women in terms of mortality deficits, but this is not guaranteed unless screening becomes routine practice and high-quality therapeutic intervention and follow-up occurs as well.