Purpose: In light of breast density legislation and discussions about supplemental screening it is important to know not only one's risk of breast cancer, but particularly the risk of a tumor that is not detected through mammographic screening. We investigated the relationship between volumetric breast density and the risk of screen-detected and interval cancer within a digital mammography (DM) screening program.
Methods: Mammographic density was automatically assessed with Volpara version 1.5.0 (Matakina, New Zealand) on the first available digital mammogram of 43,211 women (50-75 years) participating in the Dutch biennial breast cancer screening program (2003-2009). Screen-detected and interval breast cancer information was obtained from the screening registration system and through linkage with the Netherlands Cancer Registry. We estimated risks of screen-detected and interval cancers in relation to breast density using multinomial logistic regression analysis (adjusted for age). No other confounders were available in this routine screening database.
Results: 413 screen-detected and 150 interval tumors were identified. Screen-detected breast cancer risk was significantly higher in the higher breast density categories compared to the lowest (OR: 1.65, 95% CI: 1.21-2.24, OR: 1.78, 95% CI: 1.29-2.47, OR: 1.69, 95% CI: 1.08-2.63, for density categories 2 to 4 respectively compared to 1). Interval cancer risk increased with increasing breast density (OR: 2.45, 95% CI: 1.20-4.99, OR: 5.24, 95% CI: 2.59-10.59 and OR: 6.86, 95% CI: 3.12-15.11, for density categories 2 to 4 respectively compared to 1). The relationship with interval cancers was statistically significantly stronger than with screen-detected cancers (p<0.01) for density categories 3 and 4.
Conclusions: Although higher breast density is related to a higher risk of a screen-detected breast cancer, it is particularly strongly related to the risk of a breast cancer that is not detected through mammographic screening (interval cancer).