Percentage mammographic density or absolute breast density for risk stratification in breast screening: Possible implications for socioeconomic health disparity.

Objectives: Obesity levels and mortality from breast cancer are higher in more deprived areas of the UK, despite lower breast cancer incidence. Supplemental imaging for women with dense breasts has been proposed as a potential improvement to screening, but it is not clear how stratification by percentage mammographic density (%MD) would be reflected across socioeconomic groups. This study aims to clarify the associations between breast composition (dense and fatty tissue) and socioeconomic status in a multi-ethnic screening population.

Methods: Demographic characteristics were collected for 62,913 participants in a UK breast screening programme (age, ethnicity, Index of Multiple Deprivation (IMD)). Automated mammographic measurements were derived: dense volume (DV), non-dense volume (NDV) and percent density (%MD). Correlations between deprivation and mammographic composition were examined before and after adjustment for age, ethnicity and NDV, using non-dense breast volume as a proxy for body mass index (BMI).

Results: There was negligible correlation between deprivation and DV (r = 0.017; P < 0.001 in all cases), but NDV increased with increasing deprivation (Pearson r = 0.101). Correlations were weaker in the Asian and Chinese ethnic groups. %MD decreased with deprivation (r = -0.094) and adjustment for ethnicity did not alter the association between %MD and IMD (relative change, most to least deprived quintile IMD: 1.18; 95% confidence interval: 1.16, 1.21).

Conclusions: Deprivation-related differences in %MD in the screening population are largely explained by differences in breast fat volume (NDV) which reflects BMI. Women in more deprived areas, where obesity and breast cancer mortality rates are higher, have increased breast adiposity and may miss out on risk-adapted screening if stratification is based solely on %MD or BIRADS classification.