Mammographic breast density by area of residence: possible evidence of higher density in urban areas.

OBJECTIVES: A comparison of mammographic breast densities of women living in London with those of women living in rural and suburban areas. DESIGN AND METHODS: Using the standard four American College of Radiology Breast Imaging Reporting and Data System (BIRADS) categories of mammographic density, 318 mammograms of women from London and 654 mammograms of women from outside the capital aged 27-87 years who had received mammography at the Princess Grace Hospital, London, were assessed for density. The association between having any dense tissue and area of residence was assessed using both ordered and standard logistic regression, giving odds ratio estimates of relative risk of dense tissue adjusting for age.
RESULTS: Adjusting for age, London residents had significantly higher levels of density (OR = 1.32, 95% CI 1.04-1.70, p = 0.02). The major difference occurred in the age group 45-54 years and was most strongly manifested as a higher rate in London for density of 25% or more (BIRADS categories 2-4) as compared to almost entirely fatty (BIRADS 1) (OR = 2.22, 95% CI 1.05-4.68, p = 0.035).
CONCLUSION: The higher density is likely to be due to a different prevalence of risk factors in the London population. This study cannot ascertain the reason for the higher density in this urban population, but the result is a cause for concern given that screening uptake is lower in London. Increased attention to screening in urban areas and attention to screening quality for dense breast tissue might be prudent.