Mammographic Densities and Breast Cancer Risk


Mammographic Densities and Breast Cancer Risk by N.F. Boyd, G.A. Lockwood, L.J. Martina, J.A. Knight, J.W. Byng, M.J. Yae and D.L. Tritchler of Division of Epidemiology and Statistics, Ontario Cancer Institute, Toronto, Canada, Division of Preventive Oncology, Cancer Care Ontario, Toronto, Canada, Imaging Research, Sunnybrook Health Sciences Centre, Toronto, Canada


Key outtakes

  • “Individuals with extensive areas of radiologically dense breast tissue on the mammogram have been found to have a risk of breast cancer that is four to six times higher than women with little or no density. In this paper, we propose a model for the relation- ship of mammographic densities”
  • “Considerable evidence now indicates that mammographic densities are strongly related to the risk of breast cancer.”
  • “Because mammographic densities are strongly related to risk of breast cancer, factors that cause mammographic density also are likely to contribute to the causes of cancer. The identification of factors that change density may lead to the development of methods for preventing breast cancer.”
  • “We propose that the risk of breast cancer associated with mammographically dense breast tissue is due to the combined effects of two processes: cell proliferation (mitogenesis), and damage to the DNA of dividing cells (mutagenesis).”
  • “An association between the mammographic pattern of the breast and risk of breast cancer was first proposed in 1976 by the late John Wolfe, using a four category classification …”
  • “…at least 15 cohort studies… have since confirmed that Wolfe’s classification of mammographic pattern is associated with variations in risk of breast cancer…”
  • “Definitions of the categories of density compared varied between studies, but all found significantly elevated summary odds ratios between extreme categories of the classification used.”
  • “Odds ratios varied between 2.8 and 6.0 for different observers and types of density, but each of the eight studies contained an odds ratio of at least 4.0.”
  • “Two studies showed persistence of increased risk associated with extensive dense tissue for at least 5 years, and one showed that risk persisted for at least 10 years.”
  • “Risk of hyperplasia was 30 times greater, and risk of atypical hyperplasia and in situ carcinoma was 8 times greater in women with extensive densities compared to those with none.”
  • “The evidence that the tissue responsible for mammographic densities is hormonally responsive comes from the consistent associations found with age, which is at least partly due to the effect of menopause, and from the observed effects of exogenous hormones on the radiology of the breast.”
  • “Mammographic densities consistently are associated with a much greater relative risk of breast cancer than are other risk factors.”
  • “…mammographic densities are associated with a much larger attributable risk of breast cancer than atypical hyperplasia or BRCA1 and BRCA2 mutations. Further, in contrast to other risk factors, mammographic densities can be changed by hormonal or dietary interventions.”
  • “…abundant evidence indicates that mammographic densities are related to risk of breast cancer from middle age onward…”
  • “Several aspects of the association of mammographic densities with breast cancer risk meet criteria for causality and suggest that mammographic densities may be closely related to factors that are important causes of this disease.”


The full paper can be found here: Click here