Differences in breast density assessment using mammography, tomosynthesis and MRI and their implications for practice.

Literature searching of PubMed highlights, through the number of articles related to breast density and also to digital breast tomosynthesis (DBT), that there is an increasing interest in breast density assessment and DBT. Indeed, searching at first the term “breast density” and then “digital breast tomosynthesis”, it is possible to note a positive trend on these topics (http://www.ncbi.nlm.nih.gov). The question then arises as to why there is an interest in breast density assessment and how this relates to new modalities for breast cancer detection? The answer may be that modern medicine is rapidly moving towards a personalised or tailored approach based on predefined risks of a particular disease, a concept that is particularly applicable to breast cancer. Identifying females with an increased risk of developing breast cancer is possible and is important because they may benefit from modified screening and diagnostic protocols [1]. The inclusion of breast density assessment in statistical models such as the Gail et al [2] and Claus et al [3] models may improve their accuracy or use because these methods include non-modifiable risk factors, such as age at inclusion, age at menarche, age at first full-term pregnancy, number of previous biopsies with a benign result and number of first-degree relatives with breast cancer. By contrast, breast density is considered to be an independent risk factor [4], and it is also indicative of changes in modifiable risk factors [5–9]. Moreover, breast density may be particularly suitable for individualised breast cancer risk estimation and not for population-level brief estimation only [10]. Breast density assessment may be carried out using different imaging modalities used in clinical practice, such as mammography, DBT and MRI. These commonly used imaging techniques may give similar results for density assessment, but they may not always be interchangeable for an individualised purpose [11]. Therefore, the purpose of this article is to give a brief overview on breast density percentage assessment with these imaging techniques, highlighting our perspectives on the differences and limitations of each technique.