Statistical analysis of mammographic breast composition measurements: towards a quantitative measure of relative breast cancer risk.

OBJECTIVE: A number of studies have identified the relationship between the visual appearance of high breast density at mammography and an increased risk of breast cancer. With the advent of digital mammography and the promise of routine measurements of parameters associated with breast composition, the possibility arises of using breast composition in a quantitative manner to predict relative breast cancer risk. Previous measurements have shown that the average proportion of glandular and adipose tissue within the breast varies with both age and breast size. In order to be able to identify individual women with an unusually high volume of glandular tissue, it will therefore be necessary to make comparisons with a disease-free population matched for age and breast size.
METHODS: A large number of breast glandular thickness measurements were analysed to investigate the statistics of breast composition across a disease-free population as a test of a suitable methodology for relative risk estimation. The large data set is also used to revisit the trends in breast composition used in the current UK method of breast radiation dosimetry.
RESULTS: It is demonstrated that a non-linear transformation can be used to produce normal statistical distributions, suitable for producing a standardised "Z-score" for breast composition.
CONCLUSION: A standard "Z-score" approach to identify women with unusually glandular breasts is recommended and so provide a basis for cancer risk estimations.