Breast density is a hot topic in Australia right now, as it should be—international research has shown that women with dense breasts have a significant increase in the risk of developing breast cancer and an increase in the risk of cancer being missed at screening. You may be aware that not-for-profit awareness organisations such as Pink Hope are campaigning alongside academic groups to promote conversations on the importance of women knowing their breast density. Not only do these campaigns indicate wider acceptance of breast density’s significance, they also reflect the accumulating clinical evidence supporting more targeted screening practices for women at different breast densities.
Breast density levels vary considerably
Breast density is best described as the proportion of the breast made up of fibrous or glandular tissue versus fatty tissue, as seen on a mammogram—and it varies considerably between women and over time.
Since 1998, the American College of Radiology (ACR) has been segmenting density into four broad categories: “almost entirely fatty”, “scattered fibroglandular tissue”, “heterogeneously dense”, and “extremely dense”.
For many Australian women, this information will be new, as Western Australia is the only state requiring that women be given any information about their density.
In a typical Western population, 10 percent of women have “almost entirely fatty” breasts; 40 percent have “scattered fibroglandular tissue”; 40 percent have “heterogeneously dense” breasts, which can make it hard to see small tumours on a mammogram; and 10 percent have “extremely dense” breasts, a density level which, as noted by the ACR, “lowers the sensitivity of mammography.”
Each of these categories has a very different risk profile, suggesting the need for personalised screening programs. For instance, for women with medium-density breasts, tomosynthesis (3D mammography) is reported to help detect cancer compared to 2D mammography, but for women with “extremely dense breasts” (at the greatest risk of missed cancer) the evidence supporting tomosynthesis is far less compelling, and other supplemental modalities such as ultrasound may be more beneficial.
For simplicity, media and other stakeholders often reduce density levels to just two categories, “fatty” and “dense”. This gross oversimplification has led to a debate as to the value and plausibility of personalised screening when fully half the population are considered “dense” and therefore potentially need costly additional screening. For Australia’s free national screening program, which provides 2D mammography (breast x-ray) to around 800,000 women each year, offering further personalised screening in the form of 3D tomosynthesis, ultrasounds, or MRIs to 400,000 of those women is likely to prove too expensive.
Let’s start with the densest 10 percent
If we reconsider the ACR’s four categories, then a more cost-effective and practical approach is to start by addressing the needs of those women at the greatest risk of missed breast cancer (and likely higher risk of developing cancer). Referring the top 10 percent—or 80,000 women—appears more viable than referring the top 50 percent. It would allow the necessary systems to be put in place around density, to establish a base ready for a second stage of personalisation that could include full risk assessment using a tool such as Tyrer-Cuzick v8 with our world-leading automated density classification software, VolparaDensity.
This is the approach being taken by a major Dutch study, targeting the top 10 percent of women with dense breasts as judged by VolparaDensity software. The trial, which commenced in 2011, is using breast MRIs for women in the highest masking risk category and is expected to start reporting results later this year. Of course, because VolparaDensity provides a clinically proven continuous measure of breast density, the Dutch, or others, could have opted for the top 5 percent or top 15 percent according to capacity.
It’s clear that mammograms, though proven to save lives and very effective in fatty breasts, are not enough on their own for women with “extremely dense” breasts. Therefore, is it not time we get started in countries with public screening programs, such as Australia, by focusing on the women at greatest risk?