REPORTS Breast Density as a Predictor of Mammographic Detection: Comparison of Interval- and Screen-Detected Cancers

is the best method to reduce mortality from breast cancer, yet some breast cancers cannot be detected by mam-mography. Cancers diagnosed after a negative mammogram are known as interval cancers. This study investi-gated whether mammographic breast density is related to the risk of interval cancer. Methods: Subjects were se-lected from women participating in mammographic screening from 1988 through 1993 in a large health mainte-nance organization based in Seattle, WA. Women were eligible for the study if they had been diagnosed with a first primary invasive breast cancer within 24 months of a screening mammogram and before a subsequent one. Interval cancer case subjects (n = 149) were women whose breast cancer occurred after a negative or benign mammo-graphic assessment. Screen-detected control subjects (n = 388) were diag-nosed after a positive screening mam-mogram. One radiologist, who was blinded to cancer status, assessed breast density by use of the America