Comparison of Mortality Among Participants of Women’s Health Initiative Trials With Screening-Detected Breast Cancers vs Interval Breast Cancers

Key Points Question Is the length of the interscreening period associated with breast cancer prognostic factors and mortality in interval breast cancers compared with cancers detected by screening? Findings In this study using data from the Women’s Health Initiative, a national study among postmenopausal women, interval breast cancers diagnosed within 1 year from a mammogram with negative results were associated with worse breast cancer–specific mortality compared with breast cancers detected by screening. Mortality remained statistically significantly higher after adjustment for trial group, molecular subtype, other risk factors, histologic characteristics, and either tumor size or lymph node but not when tumor size and lymph node were included in the model; no differences were observed between interval cancers diagnosed between 1 and 2.5 years from a mammogram with negative results and breast cancers detected by screening. Meaning Interval cancers occurring within 1 year from a mammogram with negative results may have a unique biology that accounts for aggressive features.