Ethnic and age differences in right-left breast asymmetry in a large population-based screening population.

Abstract

OBJECTIVES Exposure to sex hormones is important in the pathogenesis of breast cancer (BC) and inability to tolerate such exposure may be reflected in increased asymmetrical growth of the breasts. This study aims to characterise, for the first time, asymmetry in breast volume (BV) and radio-dense volume (DV) in a large ethnically-diverse population. METHODS Automated measurements from digital raw mammographic images of 54,591 cancer-free participants (aged 47-73) in a UK breast screening programme were used to calculate absolute (cm3) and relative asymmetry in BV and DV. Logistic regression models were fitted to assess asymmetry associations with age and ethnicity. RESULTS BV and DV absolute asymmetry were positively correlated with the corresponding volumetric dimension (BV or DV). BV absolute asymmetry increased, whilst DV absolute asymmetry decreased, with increasing age (P-for-linear-trend<0.001 for both). Relative to Whites, Blacks had statistically significantly higher, and Chinese lower, BV and DV absolute asymmetries. However, after adjustment for the corresponding underlying volumetric dimension the age and ethnic differences were greatly attenuated. Median relative (fluctuating) BV and DV asymmetry were 2.34 and 3.28% respectively. CONCLUSIONS After adjusting for the relevant volumetric dimension (BV or DV), age and ethnic differences in absolute breast asymmetry were largely resolved. ADVANCES IN KNOWLEDGE Previous small studies have reported breast asymmetry - BC associations. Automated measurements of asymmetry allow the conduct of large-scale studies to further investigate these associations.