B31
The spatial distribution of radiodense breast tissue: a longitudinal study
Snehal Pinto Pereira1, Valerie McCormack3, Sue Moss2, Isabel dos Santos Silva1
1London School of Hygiene and Tropical Medicine, London, UK, 2The Institute of Cancer Research, Sutton, UK, 3International Agency for Cancer Research, Lyon, France
Mammographic breast density is one of the strongest known markers of susceptibility to breast cancer. Research into density has relied on a single measure (e.g. percent density) summarising the average level of density for the whole breast, with no consideration to the distribution of radiodense tissue. We investigated the spatial distribution of density within the breast using 493 mammographic images from a sample of 165 pre-menopausal women.
Each breast image was divided into 48 regions and percent density (PD) for the whole breast (overall PD) and for each one of its regions (regional PD) was estimated. The spatial autocorrelation (Morans I) of regional PD for each image was calculated to investigate spatial clustering of density, whether the degree of clustering varied between a womans two breasts and whether it was affected by age and other density correlates.
The median Moran's I value for 165 women was 0.31 (inter-quartile range: 0.26, 0.37) indicating a clustered pattern. High density areas tended to cluster in central breast regions, regardless of the overall PD level, but with considerable between-woman variability in regional PD. The degree of clustering was similar between a womans two breasts and did not change with aging (mean within-woman difference in I values between breasts/screens: 0.00 (95% confidence interval (CI): -0.01, 0.01; p=0.76) and 0.01 (95% CI: -0.01, 0.02; p=0.30) respectively). Neither parity nor age at first birth affected the spatial autocorrelation level, but increasing BMI was associated with a decrease in the degree of spatial clustering.
We demonstrated that the distribution of radiodense tissue within the breast is spatially autocorrelated, generally with high density areas clustering in the central breast regions. The degree of clustering was similar within a womans two breasts and between women, and was little affected by age or reproductive factors although it declined with increasing BMI.
