Survival and Disease-Free Survival by Breast Density and Phenotype in Interval Breast Cancers.

We aimed to evaluate survival and disease-free survival in different subtypes of interval cancers by breast density, taking into account clinical and biological characteristics. We included 374 invasive breast tumors (195 screen-detected cancers; 179 interval cancers, classified into true interval, false-negatives, occult tumors and minimal-sign cancers) diagnosed in women ages 50-69 years undergoing biennial screening from 2000-2009, followed up to 2014. Breast density was categorized into non-dense (<25% dense tissue) and mixed dense breasts (≥25%). Survival curves were generated by the Kaplan-Meier method and compared by the log-rank test. Cox proportional hazard regression models were computed to estimate the adjusted hazard ratios (aHRs) and 95% confidence intervals (95% CIs) for death and recurrences by comparing women with interval and true interval cancers versus women with screen-detected cancers, controlling for tumor and patient characteristics. All analyses were stratified by breast density. Interval cancers were detected in younger women, at more advanced stages, in denser breasts and showed a higher proportion of triple-negative cancers, especially among true interval cancers. Women with interval cancer and non-dense breasts had an aHR for death of 3.40 (95% CI, 0.92-12.62). Women with true interval cancers detected in non-dense breasts had the highest adjusted risk of death (aHR, 6.55; 95% CI, 1.37-31.39). Women with true interval cancer in non-dense breasts had a higher risk of death than women with screen-detected cancers. These results support the advisability of routinely collecting information on breast density, both for further tailoring of screening strategies and as a prognostic factor for diagnosed breast cancers. .