Mammographic Densities and Breast Cancer Risk

Authorship

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

1998

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.”

Paper

The full paper can be found here: Click here

Breast Density and Parenchymal Patterns as Markers of Breast Cancer Risk: A Meta-analysis

Authorship

Breast Density and Parenchymal Patterns as Markers of Breast Cancer Risk: A Meta-analysis by Valerie A. McCormack and Isabel dos Santos Silva Department of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, United Kingdom.

2006 American Association for Cancer Research.

Study scope/scale

A review of 42 articles for the main analysis. The 42 articles represent aggregate data for a total of 14,134 cases and 226,871 non-cases, arising from 17 incidence studies (6,967 cases) and 17 prevalence studies (4,983 cases) in the general population and 9 studies (2,184 cases) in symptomatic (breast cancer) populations (some studies contribute to more than one category).

Key outtakes

  • “This review explains some of the heterogeneity in associations of breast density with breast cancer risk and shows that, in well-conducted studies, this is one of the strongest risk factors for breast cancer.”
  • “Breast density, a measure of the extent of radiodense fibroglandular tissue in the breast, has the potential to be used as a predictor of breast cancer risk, to monitor risk-lowering interventions and as an intermediate end point in studies of breast cancer etiology. More than 40 studies have assessed associations with Wolfe grade or percentage breast density and the majority reported 2-to-6-fold increased risks for the highest compared with the lowest risk categories…”
  • “The combined data presented here confirm that breast density, measured using either Wolfe grade or percentage density, is strongly associated with breast cancer risk…”
  • “The true association may be even stronger, as nondifferential measurement error of breast density would lead to underestimation of associations.”
  • “We found little evidence of interactions between other risk factors for breast cancer and breast density. Importantly, the combined data suggest that breast density measured at both premenopausal and postmenopausal ages is a marker of subsequent breast cancer risk and that there is no clear evidence that the strength of this association differs between these ages.”
  • “The strength of the association of breast density with breast cancer risk is greater than that for most other established breast cancer risk factors, with the exception of age and some genetic factors.”
  • “…there was no threshold level below which density was not associated with risk. Shifting the entire breast density distribution downwards by a few percentage (if possible) might reduce overall breast cancer rates. Breast density may be amenable to change.”
  • “Well-conducted incidence studies suggest that increasing breast density is associated with an increased risk of breast cancer and that the magnitude of this association is 4.64-fold (3.64-5.91) for the most dense (>75%) compared with the least dense category (<5%).”
  • “This marker (breast density) has great potential to be used for research into the etiology and prevention of breast cancer.”

Paper

The full paper can be found here: Click here