Mammography screening guidelines for women 40 to 49 and over 65 years old.

Many organizations in the United States recommend mammography screening at 1- to 2-year intervals for those 40 to 49 years old. In most areas of Canada and Europe, screening mammography is not recommended for women 40 to 49 years old. These differences have arisen over interpretation of data from the Health Insurance Plan (HIP) study and the Breast Cancer Detection Demonstration Project (BCDDP). The apparent benefit in the HIP study is probably attributable to poor survival of control subjects with stage 1 cancers. In the BCDDP, although high cancer detection rates by mammography and improved survival of patients with screen-detected cancer were seen, the latter was probably largely due to lead time bias. The screening studies in Canada and Europe show no evidence of effectiveness of mammography screening in women 40 to 49 years old, at least in the first 10 years after screening is initiated. For women over 65 there are few data, but screening to age 74 is probably appropriate.